Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large bowl, combine ground beef, breadcrumbs, egg, garlic, green onions, Korean BBQ sauce, soy sauce, sesame oil, ginger, and pepper.
Mix until just combined, then roll mixture into 1-inch meatballs and place on prepared baking sheet.
Bake for 15-18 minutes or until fully cooked through.
While meatballs are baking, prepare the spicy mayo dip by mixing mayonnaise, sriracha, and lime juice in a small bowl.
Serve meatballs hot, garnished with sesame seeds and extra green onions, with the spicy mayo dip on the side.