In a large mixing bowl, combine the ground beef, breadcrumbs, chopped green onions, egg, soy sauce, hoisin sauce, grated ginger, minced garlic, sesame oil, brown sugar, rice vinegar, sriracha (if using), and a pinch of salt and pepper. Mix everything together until well combined, but be careful not to overmix—this keeps your meatballs tender.

Using your hands, form the beef mixture into small balls, about one to two inches in diameter. Place the meatballs on a baking tray lined with parchment paper for easy cleanup.

Preheat your oven to 400°F (200°C). Bake the meatballs for about 20 minutes or until they are fully cooked through and browned on the outside, turning them halfway to ensure even cooking.

While the meatballs are baking, make the sauce. In a small saucepan, combine some additional soy sauce, hoisin sauce, brown sugar, and a splash of rice vinegar over medium heat. Stir until the sugar dissolves and the sauce thickens slightly.

Once cooked, toss the meatballs in the sauce and serve hot. Garnish with additional chopped green onions or sesame seeds if desired!