With a small, sharp paring knife score the steak on both sides.
Combine the orange juice, lime juice, olive oil, garlic, chili powder, cumin and salt in the bowl of a food processor or blender; puree until smooth. Place the steak in a large, resealable plastic bag and pour the marinade over it. Press out the air, seal the bag and marinate at room temperature for at least 2 hours.
Prepare the coals on the grill until they are glowing red with a white ash around them. Drain and discard the marinade and place the steak 4 inches over the coals; sear quickly, about 3 to 4 minutes on each side.
Move the steak away from the direct heat, cover the grill and continue to cook until the internal temperature reaches 135 F, about 7 to 10 minutes longer. Remove the steak from the grill and allow to rest for 10 minutes before slicing and serving.