Preheat your oven to 400°F.
In a large mixing bowl, combine the ground beef, breadcrumbs, green onions, soy sauce, brown sugar, sesame oil, garlic, ginger, black pepper, and red pepper flakes (if using). Mix until just combined; do not overmix.
Shape the mixture into meatballs, about 1 inch in diameter, and place them on a baking sheet lined with parchment paper.
Bake for 15-20 minutes or until the meatballs are cooked through and browned on the outside.
While the meatballs are baking, prepare a dipping sauce by mixing additional soy sauce with a splash of sesame oil and a sprinkle of sesame seeds.
Once cooked, remove the meatballs from the oven and let them cool for a few minutes. Serve warm, garnished with sesame seeds and additional green onions if desired.