Place four onion wedges and a garlic clove on a double thickness of heavy-duty foil (about 12 inches square). Dot with 1 tablespoons butter and sprinkle with 1/4 teaspoons of seasoned salt. Repeat for other 3 onions.
Fold foil around onion mixture and seal tightly. Grill, covered, over medium heat for 30-35 minutes or until onions are tender. Open foil carefully to allow steam to escape.