Meanwhile, in a large kettle, combine the soup, cream cheese, mushrooms, cream, butter and garlic powder. Stir in cheeses; cook and stir until melted. Add chicken; heat through. Drain fettuccine; add to the sauce.
Transfer to a shallow greased 2-1/2-qt. baking dish. Combine topping ingredients; sprinkle over chicken mixture. Cover and bake at 350° for 25 minutes. Uncover; bake 5-10 minutes longer or until golden brown.