Cook chicken, shred or cut up. Save the broth. Cook spaghetti noodles. Dice and saute onion, green pepper, celery and mushrooms in butter. Mix with shredded chicken, mushroom soup and one cup of the chicken broth. Line spaghetti on the bottom of oblong baking dish then layer chicken and cheese ending with cheese on top. Bake at 400 degrees until cheese is melted.