Preparation Prepare grill. In a shallow baking dish large enough to hold steak and onion slices in one layer whisk together vinegar, oil, and salt and pepper to taste. Add steak and onions and turn to coat with marinade. Marinate steak and onions, covered, 15 minutes. Make gremolata: In a small bowl toss together garlic, parsley, and zest. Drain steak and grill on an oiled rack set 5 to 6 inches over glowing coals 5 minutes on each side for medium-rare. Transfer steak to a cutting board and let stand 10 minutes. While steak is standing, drain onions, discarding marinade, and grill 5 minutes on each side, or until tender and golden. (Alternatively, steak and onions may be cooked in a hot well-seasoned ridged grill pan.) Slice steak thin across grain. Serve steak and onions sprinkled with gremolata.
Preparation Prepare grill. In a shallow baking dish large enough to hold steak and onion slices in one layer whisk together vinegar, oil, and salt and pepper to taste. Add steak and onions and turn to coat with marinade. Marinate steak and onions, covered, 15 minutes. Make gremolata: In a small bowl toss together garlic, parsley, and zest. Drain steak and grill on an oiled rack set 5 to 6 inches over glowing coals 5 minutes on each side for medium-rare. Transfer steak to a cutting board and let stand 10 minutes. While steak is standing, drain onions, discarding marinade, and grill 5 minutes on each side, or until tender and golden. (Alternatively, steak and onions may be cooked in a hot well-seasoned ridged grill pan.) Slice steak thin across grain. Serve steak and onions sprinkled with gremolata.