In a large resealable plastic bag set in a shallow baking dish, combine orange juice, cilantro, lime juice, cumin, salt, pepper, and garlic. Trim fat from steak and discard. Score both sides of steak in a diamond pattern by making shallow diagonal cuts at 1-inch intervals. Add steak to orange juice mixture. Seal bag; turn to coat steak. Marinate in the refrigerator for 1 to 4 hours, turning bag occasionally.

Drain steak, discarding marinade. For a charcoal grill, place steak on the rack of an uncovered grill directly over medium coals. Grill until desired doneness, turning once halfway through grilling. For skirt steak, allow 8 to 10 minutes. For flank steak, allow 10 to 12 minutes for medium-rare doneness (145 degrees F) or 12 to 14 minutes for medium doneness (160 degrees F) (For a gas grill, preheat grill. Reduce heat to medium. Place steak on grill rack over heat. Cover and grill as above.)

To serve, thinly slice steak across the grain.