Preheat the oven to 400°F (200°C).
Line a baking sheet with parchment paper or lightly grease it.
In a large bowl, combine the ground beef, breadcrumbs, egg, garlic, green onions, soy sauce, ginger, black pepper, and sesame oil.
Mix until just combined.
Shape the mixture into 18 to 20 evenly sized meatballs.
Arrange the meatballs on the prepared baking sheet.
Bake for 15 to 18 minutes, or until cooked through.
Meanwhile, combine the soy sauce, brown sugar, beef broth, hoisin sauce, garlic, ginger, and sesame oil in a large skillet.
Bring the sauce to a gentle simmer over medium heat.
Whisk together the cornstarch and water until smooth.
Stir the slurry into the sauce and cook until slightly thickened.
Add the cooked meatballs to the skillet and gently toss until evenly coated.
Simmer for 2 to 3 minutes.
Garnish with sliced green onions and sesame seeds before serving.