Preheat your oven to 400°F and line a large baking sheet with parchment paper for an easy release and minimal cleanup. Lightly brush or spray the parchment with a bit of oil to prevent sticking.

In a spacious mixing bowl, combine the ground beef, breadcrumbs, chopped onion, green onions, egg, soy sauce, brown sugar, garlic powder, salt, and black pepper. Mix thoroughly until the ingredients are well incorporated and the mixture holds together cohesively.

Scoop out about two spoonfuls of the beef mixture per portion and roll into meatballs approximately 1.5 inches in diameter. Arrange them evenly on the prepared baking sheet, spacing them slightly apart for even cooking.

Bake in the preheated oven for 15 minutes or until the meatballs are fully cooked through. The internal temperature should reach 160°F when measured with a meat thermometer. Once done, remove from the oven and set aside.

In a medium-sized bowl, combine the rice vinegar, soy sauce, brown sugar, honey, minced garlic, cornstarch, and water. Whisk the mixture until the sugar and cornstarch are fully dissolved and the sauce is smooth.

Pour the mixture into a shallow saucepan and bring it to medium heat. Stir continuously as the sauce simmers for about 3 to 4 minutes, allowing it to thicken into a rich, glossy glaze.

Add the baked meatballs to the saucepan and gently toss to coat each one generously with the sticky honey garlic sauce. Once evenly glazed, garnish with a sprinkle of chopped green onions and sesame seeds.

Serve hot, either as a standalone dish or accompanied by steamed jasmine rice, fried rice, or even noodles for a heartier meal.