3/4-pound piece flank steak
4 – 1/3-inch-thick slices red onion, secured with wooden picks
1 1/2 tablespoons balsamic vinegar
1/4 cup olive oil
1 small garlic clove, minced
2 tablespoons fresh parsley leaves, minced
1/2 teaspoon freshly grated orange zest
Prep Day: In a freezer bag 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, freeze.
Serve Day: Thaw. 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.
To make gremolata:
In a small bowl toss together garlic, parsley, and zest.