Simple Creamy Chicken and Spaghetti Squash Casserole

If you’re looking for a wholesome, comforting dinner that doesn’t feel heavy, this chicken and spaghetti squash casserole is the perfect solution. Tender shredded chicken is baked together with roasted spaghetti squash and a creamy, flavorful sauce for a dish that’s satisfying, family-friendly, and surprisingly easy to make. It has all the cozy casserole vibes you love, but with a lighter twist that makes it perfect for weeknight dinners or meal prep.

Reasons Why You’ll Love This Recipe

• High in protein – Shredded chicken makes this meal filling and satisfying.
• Great for meal prep – It reheats beautifully, making it perfect for lunches or busy weeknights.
• Low-carb friendly option – Spaghetti squash is a great alternative to pasta for those watching carbs.
• Naturally gluten-free – As long as your ingredients are certified gluten-free, this recipe works well for gluten-sensitive diets.
• Easy to customize – Add veggies like spinach, mushrooms, or broccoli, or swap in rotisserie chicken to save time.
• Freezer-friendly potential – Many casseroles can be prepped ahead and frozen for later.
• One-dish dinner – Everything bakes together in one pan for easier cleanup (always a win).

Ingredients You’ll Need For This Recipe

• Olive Oil – Used to roast the spaghetti squash or lightly grease the baking dish, adding subtle richness and preventing sticking.
• Sour Cream – Adds creamy tanginess to the casserole and helps create a smooth, comforting texture throughout.
• Pesto – Brings bright, herby flavor that pairs beautifully with chicken and adds depth to the creamy base.
• Parmesan Cheese – Adds salty, nutty flavor and enhances the savory richness of the dish.
• Mozzarella Cheese – Melts into gooey, stretchy perfection on top, giving the casserole that classic cheesy finish.
• Salt – Enhances all the flavors and balances the creaminess of the sauce.
• Black Pepper – Adds mild warmth and a subtle kick without overpowering the dish.
• Garlic Powder – Infuses the casserole with savory garlic flavor that blends evenly throughout.
• Cooked Chicken (or Rotisserie Chicken) – Provides hearty protein and makes this casserole filling and satisfying; rotisserie chicken is a great shortcut for convenience.
• Cooked Spaghetti Squash – Acts as a lighter, low-carb base that mimics pasta while keeping the casserole wholesome and balanced.

How to Make This Chicken and Spaghetti Squash Casserole

Preheat your oven to 375°F. Carefully slice the spaghetti squash in half lengthwise and scoop out the seeds.

Drizzle the inside with olive oil and season with salt and pepper, then place the squash cut side down on a baking sheet.

Roast for 35–40 minutes, or until the flesh is tender and easily shreds with a fork. (This is also a great recipe to make if you already have leftover cooked spaghetti squash on hand.)

Once cooked, use a fork to scrape the squash into strands and measure out about 2 cups for the casserole.

Reduce the oven temperature to 350°F.

In a 9×9 baking dish, combine the sour cream, a spoonful of pesto, grated Parmesan cheese, shredded mozzarella cheese, salt, black pepper, and garlic powder, stirring until well mixed.

Add in chopped cooked chicken—leftover chicken or rotisserie chicken both work perfectly—along with the 2 cups of cooked spaghetti squash.

Stir everything together until evenly coated. Top with an extra sprinkle of mozzarella and a few dollops of pesto over the top.

Bake for about 25 minutes, or until the cheese is melted, bubbly, and lightly golden. Let it rest for a few minutes before serving.

Storage Tips For This Recipe

Fridge Storage

• Store in an airtight container for up to 4 days.
• If you can, let it cool completely before sealing so condensation doesn’t build up (that’s what makes squash watery).
• If it’s super saucy/creamy, it actually reheats really well.

Freezer Option

• Freeze in individual portions (makes life easier).
• Store up to 2–3 months.
• Thaw overnight in the fridge before reheating.

Heads up: spaghetti squash releases water when frozen, so after reheating you might want to drain off a little liquid or stir it well.

Reheating Tips (this matters)

• Stovetop > microwave if you want the best texture. Add a splash of broth, milk, or cream while reheating to bring it back to life.
• If microwaving, reheat in 30–45 second bursts and stir in between.
• If it has cheese? A quick broil at the end = chef moment.

Common FAQ’s Related to This Recipe

• Can I use rotisserie chicken for this recipe?
  • Yes! Rotisserie chicken works perfectly and makes this recipe even quicker. Just chop or shred it before mixing it into the casserole.
• Do I need to salt the spaghetti squash before baking it?
  • Yes, lightly salting it before roasting helps draw out moisture and enhances the flavor.
• How do I know when spaghetti squash is done cooking?
  • It’s ready when the flesh is fork-tender and easily shreds into spaghetti-like strands.
• Can I make this recipe with leftover cooked spaghetti squash?
  • Absolutely. If you already have cooked squash, this casserole comes together even faster.
• Why is my spaghetti squash watery?
  • Spaghetti squash naturally holds a lot of moisture. Roasting it cut-side down and letting it cool slightly before mixing helps reduce excess water.
• Can I substitute Greek yogurt for sour cream?
  • Yes, plain Greek yogurt is a great substitute and adds extra protein while keeping it creamy.
• What type of pesto works best?
  • Traditional basil pesto works beautifully, but sun-dried tomato pesto would also be delicious for a deeper flavor.
• Can I use a different cheese?
  • Definitely. Monterey Jack, provolone, or even a little sharp cheddar can work depending on your flavor preference.
• Is this recipe low carb?
  • Yes! Spaghetti squash is a lower-carb alternative to traditional pasta, making this a lighter option.
• Can I make this ahead of time?
  • Yes. Assemble the casserole, cover, and refrigerate up to 24 hours before baking. Add a few extra minutes to the bake time if cooking straight from the fridge.

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