Trim excess fat from meat and discard. In a shallow baking dish, whisk together wine, oil, lime juice, and red pepper flakes. Add meat, turning to coat on both sides. Top with onion and pepper strips, cover and refrigerate. Marinate 20 minutes, up to 1 hour, on each side, turning once.
Prepare barbeque. Place marinated meat on grill over hot coals. Add marinated vegetables to grilling basket, place on grill. Grill meat and vegetables until cooked. Remove from grill, set aside. Place tortillas on grill, a few seconds on each side, to warm.
Add salt and pepper to meat, to taste, slice into thin strips and place on heated cast-iron skillet or large serving platter. Top with grilled onions and peppers. Serve with warmed flour tortillas and Pico de Gallo.
