Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.
In a mixing bowl, combine the ground beef, breadcrumbs, green onions, egg, garlic powder, ginger powder, salt, and black pepper. Mix until well combined.
Form the mixture into small meatballs, about 1 inch in diameter, and place them on the prepared baking sheet.
Bake the meatballs in the preheated oven for 15 minutes or until cooked through.
While the meatballs are baking, prepare the sauce. In a large skillet, heat the vegetable oil over medium heat. Add the minced garlic and grated ginger, sauté for 1 minute until fragrant.
Pour in the soy sauce and brown sugar, stirring to combine. In a small bowl, mix the cornstarch with water until smooth. Add the cornstarch mixture to the sauce, stirring continuously until the sauce thickens (about 2-3 minutes).
Once the meatballs are done baking, add them to the skillet with the sauce, gently coating them in the glaze. Simmer for an additional 2-3 minutes to allow the flavors to meld.
Serve the Mongolian meatballs hot, garnished with additional green onions if desired. Enjoy!