Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper and lightly spray with cooking oil.

In a large mixing bowl, combine ground beef, panko breadcrumbs, egg, minced garlic, grated ginger, chopped green onions, soy sauce, sesame oil, black pepper, and salt. Mix until just combined, avoiding overworking the meat.

Shape mixture into 20-24 meatballs, about 1.5 inches in diameter. Place on prepared baking sheet, spacing about 1 inch apart.

Bake for 18-20 minutes until cooked through and lightly browned, reaching an internal temperature of 160°F.

While meatballs bake, prepare the glaze. In a medium saucepan, combine soy sauce, brown sugar, honey, rice vinegar, sesame oil, garlic, ginger, and red pepper flakes. Simmer over medium heat until sugar dissolves.

Mix cornstarch with water to create a slurry. Slowly pour into simmering glaze while whisking constantly. Cook 2-3 minutes until thickened to a syrupy consistency.

Transfer cooked meatballs to a large skillet or clean pan. Pour thickened glaze over meatballs and toss gently to coat evenly.

Garnish with sesame seeds and sliced green onions. Optionally drizzle with spicy mayo. Serve immediately with toothpicks for appetizers or over rice for a main course.