Preheat the oven to 400°F (200°C) if baking the meatballs.
In a mixing bowl, combine ground beef, breadcrumbs, green onions, egg, minced garlic, salt, black pepper, and ground ginger. Mix well until all ingredients are thoroughly combined.
Form the mixture into meatballs around 1 inch in diameter and place them on a baking sheet lined with baking paper (if using).
Bake the meatballs in the preheated oven for 15-20 minutes or until cooked through (internal temperature should reach 160°F).
While the meatballs are baking, prepare the sauce. In a frying pan over medium heat, combine soy sauce, brown sugar, water, sesame oil, and red pepper flakes.
Bring the sauce to a simmer and stir occasionally until the sugar dissolves.
Add the cornstarch mixture to the sauce, stirring continuously until the sauce thickens, about 2-3 minutes. Remove from heat.
Once the meatballs are cooked, add them to the sauce in the frying pan, coating them well.
Serve the meatballs warm, garnished with additional green onions.