Prepare the marinade by mixing soy sauce, olive oil, red wine vinegar, garlic, brown sugar, pepper, salt, oregano, and rosemary.
Place the flank steak in a resealable bag and pour the marinade over it.
Seal the bag and refrigerate for at least 2 hours or overnight for best flavor.
Preheat your grill to medium-high heat.
Remove the steak from the marinade and let the excess drip off.
Discard the marinade and grill the steak for about 5-7 minutes on each side.
Use a meat thermometer to check for an internal temperature of 130°F for medium-rare.
Remove the steak from the grill and let it rest for 10 minutes.
Slice the steak against the grain into thin strips.
Serve immediately with your choice of sides.