Preheat your oven to 400°F (200°C).
In a mixing bowl, combine the ground beef, breadcrumbs, chopped green onions, milk, egg, garlic powder, ginger powder, salt, and pepper. Mix until well combined.
Shape the mixture into meatballs, about 1 inch in diameter, and place them on a baking sheet lined with parchment paper.
Bake the meatballs in the preheated oven for 15-20 minutes or until browned and cooked through. Use a meat thermometer to ensure they reach an internal temperature of 160°F (70°C).
While the meatballs are baking, prepare the sauce. In a small saucepan, combine the soy sauce, brown sugar, cornstarch, water, sesame oil, and red pepper flakes (if using).
Bring the sauce to a gentle boil over medium heat, whisking continuously until it thickens, about 2-3 minutes. Remove from heat.
Once the meatballs are cooked, transfer them to a serving dish and drizzle the sauce over the top. Toss gently to coat.
Serve warm over rice or noodles, and garnish with additional chopped green onions if desired.