Barbecued London Broil

Ingredients:
1/3c white vinegar
1/3c vegetable oil
3T packed brown sugar
3T soy sauce
2 medium onions, sliced
1 clove garlic, crushed
1/2t coarsely ground pepper
1 1/2# beef flank steak

To Prepare:
Mix all ingredients except steak; pour marinade over steak. Cover and refrigerateat least 4 hours, turning 2 or 3 times. Remove beef and onions; reserve marinade. Cover and grill beef 4 to 5 inches from medium coals, turning and brushing 2 or 3 times with reserved marinade, until desired doneness, 10-15 minutes for medium. Cook and stir onions in grill pan on grill until warm. Cut beef diagonally acrossthe grain into very thin slices; top with onions.