Cheesy chicken spaghetti bake combines tender chicken, spaghetti, and a creamy cheese sauce in a Southern family casserole. This protein-packed dish is a potluck legend that freezes beautifully for meal prep.
Preheat the oven to 350°F (175°C) and lightly butter a 9x13-inch baking dish.
Bring a large pot of salted water to a boil, add spaghetti, and cook for 1 minute less than package directions for al dente. Drain and set aside.
In a large skillet over medium heat, melt butter. Add onion and bell pepper; sauté for 3–4 minutes until softened but not browned.
Reduce heat to low, then stir in cream of chicken soup, cream cheese, milk, diced tomatoes with chilies, garlic powder, salt, pepper, and paprika. Stir until the sauce is smooth and heated through.
Combine cooked spaghetti, sauce, and shredded chicken in a large bowl. Toss to coat the pasta evenly, then fold in 1½ cups of cheddar cheese.
Transfer the mixture into the prepared baking dish. Top evenly with remaining ½ cup cheddar cheese.
Bake uncovered for 25–30 minutes, or until the cheese is melted and the casserole is lightly bubbling around the edges. Let cool for 5 minutes before serving for easiest slicing.