PREHEAT oven to 450°F. Moisten meat with water. Shake off excess. Coat meat with coating mix as directed on package. Discard any remaining coating mix.
TOSS sweet potatoes, red potatoes and onion with dressing. Spread evenly into 15x10-inch baking pan; top with meat.
BAKE 25 to 30 min. or until meat thermometer inserted in centre of meat registers 160°F, stirring vegetables after 15 min. Let stand 5 min. Slice meat. Serve with vegetables.