Heat barbecue to medium heat. Remove steak from marinade; discard marinade. Grill steak and foil packet 15 min. or until steak is cooked to medium doneness, turning steak and packet after 8 min. Remove steak from barbecue. Continue to grill packet 2 min. or until potatoes are tender. Cut slits in foil to release steam before opening packet. Top potatoes with cheese.