PREHEAT oven to 450°F. Moisten meat with water. Shake off excess. Coat meat as directed on package. Discard any remaining coating mix.
TOSS sweet potatoes, red potatoes and onion with dressing. Spread evenly into 15x10x1-inch baking pan; top with meat.
BAKE 25 to 30 minutes or until meat thermometer inserted in center of meat registers 160°F, stirring vegetables after 15 minutes. Let stand 5 minutes. Slice meat. Serve with vegetables.