In a large mixing bowl, combine ground beef, breadcrumbs, Parmesan cheese, green onions, garlic, egg, salt, black pepper, and red pepper flakes. Mix until well combined.
Shape the mixture into meatballs about the size of a golf ball and place them on a baking sheet lined with parchment paper.
Preheat the oven to 400°F. Bake the meatballs for 20 minutes or until cooked through and browned.
In a saucepan, combine soy sauce, brown sugar, cornstarch, vegetable oil, and sesame oil. Heat over medium heat, stirring until thickened, about 3-5 minutes.
Drizzle the sauce over the baked meatballs, toss to coat, and return to the oven for an additional 5 minutes.