Marinate Flank Steak overnight in lime juice and garlic, then chop up a zesty pico de gallo while the beef is on the grill. Be sure to slice steak against the grain for max tenderness.
Combine marinade ingredients in small bowl. Place beef Flank Steak and marinade in food-safe plastic bag; turn to coat. Close bag securely and marinate in refrigerator 6 hours or as long as overnight, turning occasionally.
Combine Pico de Gallo ingredients in medium bowl.
Remove steak; discard marinade. Place steak on grid over medium, ash-covered coals. Grill, covered, 11 to 16 minutes (over medium heat on preheated gas grill, 16 to 21 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally. Carve across the grain into thin slices. Serve in tortillas with Pico de Gallo.