Cut 1/2 inch off the top of an onion; peel the outer layer off and discard. Cut onion into 12 to 16 vertical wedges, leaving root base intact. Set onion on a 12x10-inch foil sheet.
Top onion with butter, thyme or oregano, rosemary, salt and pepper. Wrap foil around onion, pinching edges together tightly. Place foil packet on rack over medium heat in preheated barbeque grill and grill for 25 to 35 minutes or until juicy and tender.