Preheat Oven: Preheat your oven to 350°F (175°C).

Cook Chicken: In a large pot, bring water to a boil. Add chicken pieces and reduce heat to a simmer. Cook for 30-45 minutes until tender. Remove chicken and reserve 2 cups of broth. Allow chicken to cool, then remove skin and shred the meat to yield about 2 cups.

Cook Spaghetti: In the same pot, cook the spaghetti in the reserved chicken broth until al dente. Drain and set aside.

Combine Ingredients: In a large mixing bowl, combine cooked spaghetti, shredded chicken, cream of mushroom soup, 1 1/2 cups of cheddar cheese, green and red bell peppers, onion, seasoned salt, cayenne pepper, and additional salt and black pepper to taste. Add 1 cup of reserved broth, and mix gently to moisten, adding more if needed.

Assemble Casserole: Transfer mixture to a casserole dish. Sprinkle remaining 1 cup of cheddar cheese over the top.

Bake or Store: Bake immediately for 45 minutes or until bubbly. Cover with foil if cheese browns too quickly. Alternatively, freeze for up to 6 months or refrigerate for up to 2 days before baking.