Boil chicken in water, salt, pepper, garlic, celery and onion for 20 minutes or until chicken is no longer pink inside. Drain and reserve strained broth. cut up chicken into bite size pieces. Sautee mushrooms and onions in olive oil.
Heat soup, slowly in sauce pan. Add cheese, sour cream, chicken, mushrooms, olives and broth. Mix with drained spaghetti. Mixture should be sloppy. Add more chicken broth if mixture seems dry. Pour into casserole dish, top with extra cheese and bake at 350 degrees for 20-25 minutes or until bubbly.