Chicken Tetrazzini

1 chicken (or chicken parts), 2- 3 lb. cooked, de-boned, and chopped into bite-size pieces
1 (20 oz.) spaghetti
1 medium bell pepper, diced
1 medium onion, diced
2-3 stalks celery, diced
1 (10 oz.) sharp Cheddar cheese, shredded
1 (10 oz.) mild Cheddar cheese, shredded
1 (15 oz.) can stewed chopped tomatoes (save can to measure water)
1 can cream of mushroom soup

Boil chicken; save water to cook spaghetti. Saute in 4- 6 ounces butter or margarine, the bell pepper, onion and celery until soft and slightly browned. Put spaghetti in water to cook at this time. Add to sauteed vegetables the stewed tomatoes (chopped or placed in the blender for a short time) and add cream of mushroom soup. Stir. Then add to this 1/2 to 3/4 can of water; stir. Add chopped chicken to mixture; stir and add cheese. Simmer over very low heat (to prevent sticking) while the spaghetti finishes cooking.
Drain and rinse spaghetti and layer in very large pan with sauce; cook in a 350 oven for about 20 minutes or until bubbly. Serves 10-12 people.