2 large onions, peeled and cut lengthwise into 6 wedges, leaving root ends intact
2 1/2 tablespoons olive oil
2 1/2 teaspoons balsamic vinegar
1 1/2 teaspoons salt
1/4 cup fresh lime juice
2 lb skirt steak, halved crosswise
2 1/2 teaspoons coarsely ground black pepper
18 flour tortillas
1 cup fresh cilantro leaves
Accompaniment: tomatillo or tomato salsa; lime wedges
Special equipment: metal skewers or a grill basket
Directions
Prepare grill for cooking.
Thread onions onto skewers (or put in grill basket), then brush with 1/2 tablespoon oil and season with salt and pepper. When fire is medium-hot (you can hold your hand 5 inches above rack for 3 to 4 seconds), grill onions, turning occasionally, until tender, 16 to 20 minutes. Transfer to a cutting board. When just cool enough to handle, cut onions into 1-inch pieces and toss with vinegar and 1/2 teaspoon salt.
While onions are grilling, stir together lime juice and remaining teaspoon salt and 2 tablespoons oil in a shallow dish, then add steak and marinate at room temperature, turning once, 10 minutes.
Pat steak dry, then rub with pepper. Grill steak on lightly oiled grill rack, turning once, 6 to 10 minutes total for medium-rare. Transfer to cutting board, then let stand 5 minutes before cutting diagonally into thin slices.
While steak is standing, toast tortillas directly on grill rack, turning once, until puffed slightly and browned in spots, about 1 minute total. Serve steak, onions, cilantro, and salsa all wrapped in tortillas.
