Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
In a large mixing bowl, combine ground beef, panko, milk, egg, garlic, ginger, salt, and pepper. Mix until just combined — avoid overmixing for tender meatballs.
Form into 1-inch meatballs and arrange evenly on the prepared baking sheet.
Bake for 12–15 minutes, or until cooked through and lightly golden.
2️⃣ Make the Mongolian Sauce:
While meatballs bake, heat 1 tbsp vegetable oil in a saucepan over medium heat.
Add garlic and ginger; sauté for 30 seconds until fragrant.
Stir in soy sauce, water, brown sugar, hoisin sauce, and rice vinegar.
Bring to a gentle simmer. Add cornstarch slurry and stir constantly for 2–3 minutes until sauce thickens and turns glossy.