Leftover Turkey Tetrazzini

Cook spaghetti according to package directions. Drain and place in a greased 11x7-in. baking dish. Top with turkey; set aside., In a large skillet, saute the mushrooms and onion in butter until tender. Whisk in the soup, milk, poultry seasoning and mustard until blended. Add cheddar cheese; cook and stir over medium heat until melted. Pour over turkey., Sprinkle with mozzarella and Parmesan cheeses (dish will be full). Bake, uncovered, at 350° for 25-30 minutes or until heated through. Sprinkle with parsley.