Preheat oven to 400°F (200°C). In a bowl, mix ground beef, breadcrumbs, egg, garlic, ginger, soy sauce, sesame oil, and chili flakes. Roll into small meatballs and place on a lined baking sheet.
Bake 15–18 minutes or pan-fry until cooked through and golden.
In a saucepan, whisk soy sauce, brown sugar, garlic, ginger, gochujang, and rice vinegar. Simmer until glossy, then stir in sesame oil.
Toss cooked meatballs in glaze until evenly coated.
Warm tortillas and fill each with 2–3 meatballs. Top with slaw, cilantro, sesame seeds, and optional toppings. Serve immediately.