1Place beef in a shallow dish. In a small bowl, combine soy sauce, sugar, 1/4 cup green onion slices, garlic, sesame seeds, sesame oil, black pepper, onion powder, and red pepper powder (if using). Pour marinade over the beef. Cover dish and marinate in refrigerator for at least 1 hour or overnight.
2Preheat an outdoor grill for high heat, and lightly oil the grill grate.
3Remove beef from the marinade, and quickly grill beef about 3 to 4 minutes per side or until slightly charred and cooked through.
4Garnish servings with remaining 1 tablespoon of sesame seeds and remaining 1/4 cup sliced green onion.