Preheat the oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish.

Bring a large pot of salted water to a boil. Cook spaghetti until just al dente, then drain and set aside.

In a large skillet over medium heat, heat butter or olive oil. Sauté diced onion and bell pepper for 3–4 minutes until softened. Add minced garlic and cook 30 seconds.

In a large bowl, combine sautéed vegetables, cream of mushroom soup, cream of chicken soup, diced tomatoes with green chilies (undrained), chicken broth, 1 1/2 cups shredded cheddar, salt, black pepper, and paprika. Stir until smooth. If using, mix in a few tablespoons of cream cheese or sour cream for extra creaminess.

Add the cooked spaghetti and shredded chicken to the bowl. Toss until the pasta is evenly coated.

Transfer the mixture to the prepared baking dish and spread into an even layer. Sprinkle the remaining 1/2 cup cheddar over the top.

Bake uncovered for 25–30 minutes, until hot, bubbly, and lightly golden on top.

Let rest 5 minutes. Garnish with parsley or green onions if desired and serve warm.