Preheat your oven to 400°F.
In a large bowl, combine the ground beef, breadcrumbs, green onions, garlic, soy sauce, sesame oil, brown sugar, ginger, black pepper, and egg. Mix until well combined.
Form the mixture into meatballs, about 1 inch in diameter, and place them on a baking sheet lined with parchment paper. Sprinkle sesame seeds on top of each meatball.
Bake in the preheated oven for 20-25 minutes, or until the meatballs are cooked through and browned.
While the meatballs are baking, prepare the spicy mayo dip by mixing together the mayonnaise, sriracha sauce, and lime juice in a small bowl. Adjust the sriracha to taste for desired spiciness.
Serve the meatballs hot with the spicy mayo dip on the side.