Step 1: Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.
Step 2: In a large bowl, combine ground beef, panko breadcrumbs, egg, minced garlic, grated ginger, 1 tbsp soy sauce, 1 tbsp sesame oil, and black pepper. Mix gently until just combined, being careful not to overmix.
Step 3: Roll the mixture into 1-inch meatballs and place them on the prepared baking sheet.
Step 4: Bake for 20-25 minutes, or until cooked through and lightly browned.
Step 5: While meatballs bake, prepare the Korean BBQ glaze. In a small saucepan, whisk together gochujang, 1/4 cup soy sauce, brown sugar, 2 tbsp rice vinegar, 1 tbsp sesame oil, minced garlic, and grated ginger. Bring to a simmer over medium heat and cook for 3-5 minutes, stirring occasionally, until slightly thickened. Remove from heat.
Step 6: Prepare the Spicy Mayo Dip by whisking together mayonnaise, 1-2 tbsp gochujang, 1 tbsp rice vinegar, 1 tsp sesame oil, and optional pinch of sugar in a small bowl. Add a teaspoon of water if you prefer a thinner consistency.
Step 7: Once meatballs are cooked, transfer them to a large bowl. Pour the Korean BBQ glaze over the meatballs and toss gently to coat completely.
Step 8: Serve hot, garnished with sesame seeds and chopped green onions, alongside the Spicy Mayo Dip.