Under cold running water, rinse short ribs and drain very well.
In a food processor, process pear, onions, garlic, and ginger until pureed (the texture of applesauce).
In a bowl, combine soy sauce, sugar, rice vinegar, sesame oil, salt, and pepper. Stir until sugar and salt are dissolved. Add puree pear mixture, green onions and sesame seeds. Stir until well-combined.
Add beef short ribs, massaging meat. Cover and marinate in the fridge for at least 4 hours or overnight for best results. Drain ribs from marinade and bring to room temperature.
Heat the grill to high. Arrange short ribs in a single layer on hot grill and grill for about 2 to 4 minutes on each side or until slightly charred and tender. Cut between bones, if desired.