In a large bowl, combine orange juice, lime juice, minced garlic, olive oil, ground cumin, chili powder, salt, and black pepper. Mix well.
Place the flank steak in a plastic bag or shallow dish and pour the marinade over the meat. Make sure it is well coated. Marinate in the refrigerator for at least 1 hour, or up to 8 hours.
Preheat a grill or grill pan to high heat. Remove the steak from the marinade and shake off excess marinade.
Grill the steak for 7-10 minutes per side, or until it reaches your desired level of doneness. Allow the steak to rest for 5 minutes before slicing.
Slice the steak against the grain into thin strips. Garnish with chopped cilantro and serve!