GRILL DIRECTIONS: Heat grill. Cut four 18x12-inch pieces of heavy-duty foil. Place 1/4 of potatoes and onion on each piece of foil. Sprinkle each with 1/4 of parsley, salt and pepper; top each with 1 tablespoon margarine. Wrap each packet securely using double-fold seals, allowing room for heat expansion.
When ready to grill, place foil packets on gas grill over medium heat or on charcoal grill 4 to 6 inches from medium coals. Cook 45 to 55 minutes or until potatoes are tender, rearranging packets several times during cooking. Open packets carefully to allow hot steam to escape.