In a large zip top bag, combine the soy sauce, balsamic vinegar, maple syrup, garlic, salt and pepper. Massage the bag so that all the ingredients are well combined. Add the flap meat and massage the bag so that meat is well coated in the marinade. Allow the meat to marinate at room temperature. This will allow the meat to come to room temperature.

Meanwhile heat the grill to high.

Grill the meat until it has reached desired doneness, about 8 minutes for medium rare, occasionally flipping the meat. Place meat on a plate and allow to rest for 10 minutes.

Slice meat against the grain. Serve hot.