1. In a mixing bowl, combine soy sauce, olive oil, red wine vinegar, garlic, oregano, and black pepper.
2. Place the flank steak in a large resealable plastic bag. Pour the marinade over the steak, seal the bag, and refrigerate for at least 2 hours, or overnight for best results.
3. Preheat your grill to high heat. Remove the steak from the marinade and discard the marinade.
4. Grill the steak for 6-7 minutes per side, or until it reaches your desired level of doneness.
5. Let the steak rest for 5 minutes before slicing against the grain. Serve and enjoy!