Cook the spaghetti according to the package directions, then drain and set aside.
Sauté the vegetables:
In a large skillet, heat the olive oil over medium heat. Add the diced onion (and bell pepper, if using) and sauté for about 4-5 minutes, until softened.
Combine the ingredients:
To the skillet with the sautéed vegetables, add the cooked chicken, Rotel tomatoes, cream of chicken soup, sour cream, garlic powder, onion powder, paprika, and salt and pepper. Stir everything together and cook over medium heat for 5-7 minutes until it’s heated through and well combined.
Add cheese:
Stir in 1 cup of shredded cheddar cheese and mix until the cheese is melted and the sauce becomes creamy.
Combine with pasta:
Add the drained spaghetti to the skillet, tossing gently to coat the pasta in the creamy chicken mixture. If the mixture seems too thick, you can add a little bit of milk or chicken broth to reach your desired consistency.
Top with cheese and bake (optional):
If you’d like a cheesy, baked topping, preheat your oven to 350°F (175°C). Transfer the chicken spaghetti mixture to a greased 9×13-inch baking dish, then sprinkle the remaining ½ cup of shredded cheddar cheese on top. Bake for 20-25 minutes, until the cheese is melted and bubbly.
Serve:
Garnish with fresh parsley if desired, and serve hot!
