Remove steaks from marinade; discard marinade. Place steaks in center of grid over medium, ash-covered coals. Arrange onion and pepper around steaks. Grill steaks, covered, 7 to 12 minutes (over medium heat on preheated gas grill, 8 to 12 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally. Grill onion and pepper 15 to 20 minutes (gas grill times remain the same) or until vegetables are tender, turning once.