1 medium onion, coarsely chopped
1 tablespoon grated lemon zest
1/4 cup fresh lemon juice
1/2 cup balsamic vinegar
2 tablespoons olive oil
3 garlic cloves, minced
1 1/2 teaspoons basil
1/2 teaspoon black pepper
1 (1 1/2 pound) London broil, cut 1 1/4 inches thick

In a shallow bowl combine, onion, lemon zest, lemon juice, vinegar, oil, mustard, garlic, basil and pepper.

Place the steak in the dish. Spoon marinade on top. Cover dish and marinate the meat for 8 hours or overnight, turning the steak every few hours.

Prepare grill. Spray with nonstick cooking spray. Remove steak from marinade and brush off any particles. Grill the meat for 7 minutes. Turn the steak grill for 7 minutes more for rare, 9 minutes for medium, 11 minutes for medium well done. Adjust time if using broiler.

Let steak stand for 5 minutes before carving.