Place steak in a shallow glass baking dish. Rub
with oil on each
side. Sprinkle with oregano, salt and pepper. Sprinkle orange juice,
lime juice, and vinegar over the steak. Cover and refrigerate
overnight for best flavor or several hours, turning occasionally.
To cook, bring meat to room temperature. Prepare and preheat charcoal
grill (or gas grill). Drain meat, reserving marinade. Place steak on
grill. Top with orange slices. Occasionally spoon reserved marinade
over steaks as they cook. Grill 3-4 minutes on each side, or until
medium-rare. Cook longer if desired. Remove orange slices to turn
steak. Replace orange slices on top of steak.