Chicken Spaghetti

A comforting, cheesy baked pasta loaded with shredded chicken, spaghetti, and a creamy tomato-cheese sauce, baked until bubbling and golden on top.

The kind of casserole that turns leftover chicken into a full new dinner.

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Prep Time
20 mins

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Cook Time
30 mins

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Servings
6 people

Why You Love This Recipe

A great way to use leftover chicken. Rotisserie chicken or leftovers from another meal work perfectly here, making this an easy way to stretch chicken into a whole new dinner.
Make-ahead and freezer friendly. This casserole can be assembled a day ahead or frozen unbaked, making it one of the easier dishes to have ready before you need it.
Comfort food the whole table will eat. The creamy, cheesy sauce and soft pasta make this an easy sell for picky eaters while still satisfying for adults.
Feeds a crowd from simple ingredients. A handful of pantry staples turn into a full 9x13 dish, making it a practical choice for potlucks or larger families.

Tools and Preparation

Essential Tools and Equipment

Large pot — for boiling the spaghetti and, separately, for poaching the chicken if not using leftovers.
Large skillet — for sautéing the onion, bell pepper, and celery, and for building the cheese sauce.
9x13-inch baking dish — the standard size for this casserole, holding the full recipe with room to bubble at the edges.
Two forks (or a stand mixer) — for shredding the chicken quickly and evenly if cooking it from raw.
Box grater — for shredding cheddar fresh, which melts more smoothly into the sauce than the pre-shredded kind.
Large mixing spoon or spatula — for folding the pasta, chicken, and sauce together without breaking up the noodles too much.

Importance of Each Tool

A large pot matters for the spaghetti specifically because the pasta needs room to move freely in boiling water, or it tends to clump and stick together before it even reaches the casserole dish.
Freshly grated cheddar makes a real difference in the final texture of the sauce, since pre-shredded cheese is coated in anti-caking starches that can leave a baked cheese sauce looking slightly separated or greasy instead of smooth.
The 9x13 baking dish is sized specifically for this volume of pasta and sauce — a smaller dish risks overflow in the oven, while a much larger one spreads the casserole too thin and can dry it out during baking.

Ingredients

This serves six as a main course, with good odds of leftovers. The recipe scales up easily for a larger gathering using two baking dishes.

For the Chicken and Pasta:

Cooked, shredded chicken (rotisserie or poached) — 3 cups
Spaghetti, broken in half — 12 oz
Kosher salt, for the pasta water — 2 tbsp

For the Sauce:

Unsalted butter — 3 tbsp
Yellow onion, diced — 1/2 cup
Green bell pepper, diced — 1/2 cup
Celery, diced — 1/2 cup
Garlic cloves, minced — 2
All-purpose flour — 3 tbsp
Chicken broth — 1.5 cups
Whole milk — 1 cup
Canned diced tomatoes, drained — 1 cup (about one 14.5 oz can)
Cream cheese, softened — 4 oz
Shredded sharp cheddar cheese, divided — 2.5 cups
Kosher salt — 3/4 tsp, or to taste
Black pepper — 1/2 tsp
Cayenne pepper (optional) — 1/4 tsp

To Finish:

Fresh parsley, chopped — for garnish
Extra shredded cheddar — for topping

Steps To Create Recipe

Cook the spaghetti. Bring a large pot of generously salted water to a boil. Cook the spaghetti according to the package instructions until just shy of al dente, since it will continue cooking in the oven. Drain and set aside.
Sauté the vegetables. In a large skillet, melt the butter over medium heat. Add the onion, bell pepper, and celery, and cook for 5 to 6 minutes, stirring occasionally, until softened. Add the garlic and cook for 30 seconds more, until fragrant.
Build the roux. Sprinkle the flour over the softened vegetables and stir constantly for 1 minute, cooking out the raw flour taste while keeping everything moving so it doesn't clump.
Add the liquid. Slowly pour in the chicken broth and milk, whisking constantly to prevent lumps. Bring to a gentle simmer and cook for 3 to 4 minutes, until the sauce thickens enough to coat the back of a spoon.
Stir in the tomatoes and cream cheese. Add the drained diced tomatoes and the softened cream cheese, stirring until the cream cheese fully melts into the sauce and everything is smooth.
Melt in the cheddar. Reduce the heat to low and stir in 1.5 cups of the shredded cheddar, a handful at a time, until fully melted and the sauce is smooth. Season with salt, pepper, and cayenne if using.
Combine everything. Preheat the oven to 350°F. In a large bowl, combine the cooked spaghetti, shredded chicken, and the cheese sauce, folding gently until everything is evenly coated.
Transfer to the baking dish. Spread the mixture evenly into a greased 9x13-inch baking dish. Sprinkle the remaining 1 cup of shredded cheddar evenly over the top.
Bake until bubbling. Bake uncovered for 20 to 25 minutes, until the cheese on top is melted and lightly golden and the casserole is bubbling at the edges.
Rest and serve. Let the casserole rest for 5 to 10 minutes before serving, which helps it set slightly for cleaner portions. Garnish with chopped parsley before serving.

How to Serve

Chicken spaghetti is a complete meal on its own, but a simple side or two rounds it out nicely.
A crisp green salad with a light vinaigrette helps balance the richness of the cheese sauce, and garlic bread is a natural addition for scooping up any extra sauce left on the plate.
For a potluck or family gathering, this casserole travels and reheats well, making it an easy dish to bring already assembled and bake on-site, or to serve straight from the dish at the table.
A simple steamed or roasted vegetable, like green beans or broccoli, adds some color and freshness alongside.
Good pairings: garlic bread, a crisp green salad, steamed green beans, roasted broccoli, sliced tomatoes with a little salt.

Common Mistakes to Avoid

Overcooking the pasta before baking. Since the spaghetti continues cooking in the oven, boiling it to full al dente beforehand often leads to mushy noodles in the finished casserole. Pull it slightly underdone.
Using pre-shredded cheddar. The anti-caking coating on packaged shredded cheese can leave the sauce looking slightly grainy or oily once baked. Freshly grated cheddar melts more smoothly into the sauce.
Skipping the roux step. Adding the broth and milk directly without first cooking the flour into the vegetables can leave the sauce thin and prone to separating in the oven. The brief roux step helps it hold together.
Not draining the canned tomatoes. Extra liquid from undrained tomatoes can make the finished casserole watery instead of creamy. Draining them well keeps the sauce at the right consistency.
Overbaking the casserole. Extended time in the oven beyond what's needed to melt the cheese and heat everything through can dry out the pasta and toughen the chicken. Watch for bubbling edges and golden cheese as your cue to pull it.
Using cold, straight-from-the-fridge chicken. Adding very cold shredded chicken can drop the overall temperature of the mixture and lead to uneven baking. Let it come closer to room temperature if time allows.

Storage & Reheating Instructions

Refrigerator: Store leftovers covered in the baking dish or in an airtight container for up to 4 days. The sauce will thicken further as it chills, which is normal.
Freezer: This casserole freezes well, both baked and unbaked. Wrap tightly and freeze for up to 3 months; thaw overnight in the refrigerator before reheating or baking.
Reheating: Cover with foil and reheat in a 350°F oven for 20 to 25 minutes, until warmed through, removing the foil for the last few minutes to re-crisp the top. Individual portions can be microwaved, though the texture is best from the oven.
Baking from frozen (unbaked): Bake covered at 350°F for about 50 to 60 minutes, removing the foil for the final 15 minutes to let the top brown.

Frequently Asked Questions

Q: Can I use rotisserie chicken for this recipe?

A: Yes, rotisserie chicken is a popular and convenient choice here. About 3 cups of shredded meat from one rotisserie chicken is roughly the right amount.

Q: Can I make this with a jarred or canned cheese sauce shortcut?

A: You can, though the homemade sauce in this recipe gives a noticeably richer, more balanced flavor. If using a shortcut, taste and adjust the seasoning since canned sauces vary in salt level.

Q: Is this dish spicy?

A: As written, it's mild, with the cayenne being entirely optional. Add more cayenne or a dash of hot sauce to the sauce if you'd like more heat.

Q: Can I assemble this ahead of time and bake it later?

A: Yes. Assemble the full casserole, cover tightly, and refrigerate for up to 24 hours before baking. Add a few extra minutes to the bake time since it will be starting from cold.

Q: Can I substitute a different pasta shape?

A: Yes, though spaghetti or thin noodles are traditional for this dish. Broken angel hair or thin egg noodles work as substitutes if that's what you have on hand.

Q: Why did my sauce turn out thin?

A: This usually means the roux step was skipped or rushed, or the canned tomatoes weren't drained well. Make sure to cook the flour briefly before adding liquid, and drain the tomatoes thoroughly.

Q: Can I make this dish without bell pepper or celery?

A: Yes, both are there mainly for texture and aromatics. You can omit either or both, though they do add a nice bit of crunch and savoriness to balance the creamy sauce.

Final Thoughts

What makes chicken spaghetti such a reliable go-to is how forgiving it is — leftover chicken, pantry staples, and a baking dish are really all it asks for, yet the result is a genuinely comforting, crowd-pleasing casserole.
Once you've made the cheese sauce once, the whole dish comes together quickly enough to become a regular fixture whenever you've got extra chicken on hand and a craving for something warm and cheesy.
This is the kind of casserole that disappears fast and gets requested again before the dish is even empty.