In a large bowl, whisk together the soy sauce, brown sugar, sesame oil, rice vinegar, garlic, ginger, green onions, sesame seeds, and black pepper until the sugar is dissolved.
Add the short ribs to the marinade, ensuring they are well coated. Cover and refrigerate for at least 4 hours, or overnight for best flavor.
Preheat your grill or broiler to medium-high heat.
Remove the short ribs from the marinade, allowing excess marinade to drip off. Discard the remaining marinade.
Grill the short ribs for about 5-7 minutes on each side, or until they are nicely charred and cooked to your desired doneness.
Let the short ribs rest for a few minutes before serving. Garnish with additional chopped green onions and sesame seeds if desired.