Sauté onion and celery in butter just until no longer crisp. Spray a casserole dish with cooking spray, layer onion and celery on bottom, arrange chicken on top, then sprinkle broken spaghetti on top of chicken. Mix soup and broth; add seasonings to taste. (A few drops of red pepper sauce is nice.) Stir in mushrooms. Pour this mixture over spaghetti. Sprinkle Parmesan cheese over all. Bake in 350° oven, covered, for 1 hour. Uncover and bake 5 to 10 minutes longer.