Combine together in a large zip top bag the sugar, soy sauce, cider, onion, apple, garlic, sesame oil, and red pepper powder. Close the bag and shake well until all ingredients are combined. Add beef short ribs, squeeze out any air left in the bag, and seal. Place the bag in the refrigerator overnight to marinate.
Heat a grill over medium high heat. Remove the short ribs from the bag and shake off excess marinade. Grill, turning once, until cooked through, approximately 4 minutes. Remove to a serving platter and garnish with sliced green onions.