Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish to prevent sticking.

In a large pot, bring salted water to a boil and cook 12 ounces of spaghetti until al dente, about 8–10 minutes. Drain and keep warm.

In a large skillet, melt 1 tablespoon of butter over medium heat. Sauté ½ cup of chopped onion, ½ cup of chopped green bell pepper, and 2 minced cloves of garlic for about 5 minutes.

In a mixing bowl, combine 1 can of cream of mushroom soup, 1 can of cream of chicken soup, 1 cup of chicken broth, and 1 cup of full-fat sour cream. Whisk until smooth.

Add 2 cups of shredded cooked chicken and the sautéed vegetables to the creamy sauce. Season with salt, black pepper, and paprika, then stir until combined.

Gently add the warm spaghetti to the chicken and sauce mixture and toss until the pasta is fully coated.

Pour the mixture into the prepared baking dish, spreading it out evenly.

Sprinkle 1 cup of shredded cheddar cheese and 1 cup of shredded mozzarella cheese over the pasta mixture.

Bake for 25–30 minutes, until the cheese is melted, bubbly, and golden on top.

Let it cool for about 5 minutes before serving.