Cheesy Chicken Spaghetti

Cook spaghetti according to box instructions and drain well.
Melt butter in large skillet over medium heat. Add onions and bell pepper and cook until starting to soften; approximately 3-4 minutes. Reduce heat to medium low. Add the minced garlic and cook for 1 additional minute. Sprinkle the vegetables with flour. Cook for 2-3 minutes; stirring frequently.
Slowly stir in the chicken broth and milk alternating between the two. Stir in drained tomatoes and ground cayenne pepper. Cook until slightly thickened; approximately 5 minutes. Stir in 2 cups shredded cheddar and grated Parmesan in small quantities until melted. Add cooked chicken and continue stirring until heated through.
Preheat oven to 350 degrees. Add cooked spaghetti to casserole dish. Pour chicken cheese sauce over the top of the spaghetti. Sprinkle with remaining cheddar cheese. Bake for 20-25 minutes or until cheese is melted and casserole is heated through.