Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large mixing bowl, combine the ground beef, breadcrumbs, chopped green onions, garlic, egg, salt, pepper, and ginger. Mix until well combined.
Form the mixture into meatballs, about 1 inch in diameter, and place them on the prepared baking sheet. Bake the meatballs in the preheated oven for 15-20 minutes, or until they are cooked through.
While the meatballs are baking, prepare the sauce. In a saucepan over medium heat, combine the soy sauce, brown sugar, rice vinegar, and sesame oil. Allow the mixture to come to a simmer, then stir in the cornstarch mixed with water. Cook until the sauce thickens, about 2-3 minutes. Remove from heat.
For the broccoli, in a non-stick skillet, heat the olive oil over medium heat. Add the broccoli florets and season with salt and pepper. Sauté for about 5-7 minutes or until the broccoli is bright green and tender-crisp.
Once the meatballs are done baking, toss them in the sauce until evenly coated.
Serve the sticky Mongolian meatballs on a plate alongside the sautéed broccoli. Drizzle any remaining sauce over the top.