In a large bowl, combine ground beef, breadcrumbs, egg, green onions, garlic, ginger, soy sauce, sesame oil, and gochujang. Mix gently until just combined.
Shape the mixture into 1–1.5 inch meatballs.
Heat a skillet with a little oil and sear the meatballs on all sides until browned.
Transfer meatballs to a baking dish. In a small bowl, mix soy sauce, brown sugar, rice vinegar, and a touch more gochujang. Pour over the meatballs.
Bake at 375°F (190°C) for 15–20 minutes until cooked through and glazed.
Mix mayonnaise and sriracha in a bowl to create the spicy mayo dip.
Serve Korean BBQ Meatballs with Spicy Mayo Dip, garnished with sesame seeds and green onions.