Step 1: Cook the Chicken & Spaghetti
If using raw chicken, boil it in salted water for 15–20 minutes, then shred it with two forks. Alternatively, use rotisserie chicken for convenience.
Cook spaghetti according to package instructions until al dente. Drain and set aside.
Step 2: Make the Creamy Sauce
In a large skillet, melt butter over medium heat. Sauté onion, bell pepper, and garlic until softened (about 3–4 minutes).
Stir in cream of chicken soup, cream of mushroom soup, and chicken broth until well combined.
Add diced tomatoes with green chilies and mix thoroughly.
Stir in shredded cheddar cheese and Velveeta cheese, stirring continuously until melted and creamy.
Add sour cream (if using), salt, black pepper, and paprika/cayenne pepper for seasoning.
Step 3: Combine Everything & Bake
In a large bowl or the same pot used for spaghetti, mix the cooked spaghetti, shredded chicken, and cheese sauce until fully coated.
Transfer to a greased 9x13 inch baking dish and spread evenly.
Top with extra shredded cheddar cheese for a golden, cheesy crust.
Step 4: Bake & Serve
Preheat oven to 350°F (175°C) and bake for 25–30 minutes until bubbly and golden brown.
Let it rest for 5 minutes before serving. Garnish with chopped parsley if desired.