Bring a large pot of water to a boil. Add the chicken pieces to the boiling water and boil for a few minutes, then return the heat to medium-low and simmer, 30-45 minutes. Remove the chicken and 2 cups of the chicken broth from the pot. When the chicken is cool, remove the skin and pick out the meat (a mix of dark and white) to make 2 generous cups.
Cook the spaghetti in the same chicken broth until al dente. Do not overcook. When the spaghetti is cooked, combine with the chicken, mushroom soup, 1 1/2 cups cheese, the green peppers, red peppers, onions, seasoned salt, cayenne, and sprinkle with salt an pepper. Stir in 1 cup of the reserved chicken cooking broth, adding an additional cup if needed.
Place the mixture in a casserole pan and top with the remaining 1 cup cheese. Cover and freeze up to 6 months, cover and refrigerate up to 2 days or bake immediately until bubbly, about 45 minutes. (If the cheese on top starts to get too cooked, cover with foil).
NOTE: Next time I make this, I will do it more quickly by buying a rotisserie chicken and using the meat from that. Cooking the chicken myself, didn't add anything to the dish.