Preheat oven to 400 F.

In a large mixing bowl, combine beef with bread crumbs, onion, green onions, egg, soy sauce, brown sugar, garlic powder, salt and pepper. Mix well to form into a uniform consistency.

Take 2 spoonfuls of beef mixture at a time and roll into 1.5-inch thick meatballs. Transfer the meatballs into a large baking pan lined with parchment paper and lightly coat with some oil to keep them from sticking, if needed.

Bake for 15 minutes until fully cooked, and set aside. The internal temperature should reach 160F, as read on a meat thermometer.

In a medium mixing bowl, add vinegar, brown sugar, soy sauce, honey, garlic, cornstarch and water. Whisk well to combine until cornstarch and sugar dissolves.

In a shallow saucepan, stir in sauce mixture and heat over medium heat for 3-4 minutes. Keep stirring until thickened to a desired consistency.

Add the meatballs to the saucepan and toss well to coat evenly. Sprinkle with green onions and sesame seeds and serve warm on its own or over a bowl of steamed rice or fried rice.