Prepare the meatballs: In a large bowl, mix the ground meat with the egg, breadcrumbs, garlic, grated onion, soy sauce, ginger, sesame oil, salt, pepper, and green onions until fully combined.
Shape: Roll into small meatballs, about 1 to 1.5 inches each.
Cook the meatballs: Heat a splash of oil in a pan and cook the meatballs until browned on all sides and cooked through.
Make the glaze: In a saucepan, combine soy sauce, honey or sugar, rice vinegar, sriracha, hoisin, garlic, and ginger. Simmer on low.
Thicken the glaze: Stir in the cornstarch slurry and cook until the glaze becomes thick, shiny, and sticky.
Coat the meatballs: Add the meatballs to the glaze and toss until fully coated.
Finish and serve: Garnish with sesame seeds, sliced green onions, and spicy mayo if desired.