Preparing the Meatballs:

1. In a large bowl, mix ground beef or turkey with garlic, ginger, green onions, soy sauce, egg, panko breadcrumbs, and cornstarch. Stir until well combined.
2. Shape the mixture into small meatballs, about 1-inch in diameter.
3. Heat vegetable oil in a large skillet over medium heat. Add the meatballs in batches, ensuring they do not overcrowd the pan.
4. Cook until golden brown on all sides and fully cooked through (about 8-10 minutes). Remove from the pan and set aside.

Making the Mongolian Sauce:

1. In a small bowl, whisk together soy sauce, hoisin sauce, brown sugar, rice vinegar, sesame oil, cornstarch, and water.
2. Pour the sauce into the same skillet used for cooking the meatballs. Stir over medium heat until the sauce thickens and becomes glossy.
3. Return the meatballs to the skillet, tossing them in the sauce until they are fully coated.

Preparing the Broccoli:

1. In a separate pan, heat vegetable oil and stir-fry the broccoli until it is bright green and crisp-tender.
2. Optionally, add a splash of water to steam the broccoli for a softer texture.

Serving:

1. Plate the Mongolian meatballs over a bed of rice or noodles, then add the cooked broccoli on the side.
2. Garnish with sesame seeds and extra green onions before serving.