Heat oven to 375°F. Cook and drain pasta as directed on package using minimum cook time.
In ungreased 2 1/2-quart casserole, mix pasta and remaining ingredients except stuffing and butter.
Cover casserole; bake 20 minutes. Uncover and stir casserole. In small bowl, mix stuffing and butter; sprinkle on top. Bake uncovered about 10 minutes longer or until hot and topping is brown.