Cut cabbage into eight wedges; place on a double thickness of heavy-duty foil (about 24 in. x 12 in.). Spread cut sides with butter. Sprinkle with onion, garlic salt and pepper.
Fold foil around cabbage and seal tightly. Grill, covered, over medium heat for 20 minutes or until tender. Open foil carefully to allow steam to escape. Yield: 8 servings.