Preheat oven to 350 degrees. Break spaghetti into thirds. Boil until al dente. Drain and set aside. In a large saucepan, heat soup over low heat. Add shredded cheese (reserve some for the top) and stir together. Add cooked, shredded chicken, mushrooms and cooked spaghetti. Add enough of the reserved broth to make it loose and liquid. Pour 1/2 mixture into baking dish. Sprinkle with reserved cheese. Pour remaining mixture over cheese. Bake 35 minutes or until bubbly.