Preheat and prep: Heat the oven to 400°F (200°C). Line a baking sheet with parchment or lightly oil it to prevent sticking.
Mix the meatball base: In a large bowl, combine ground meat, panko, egg, green onions, garlic, ginger, soy sauce, sesame oil, salt, and pepper. Use clean hands or a fork to mix until just combined. Don’t overwork the mixture or the meatballs can turn tough.
Shape the meatballs: Scoop about 1 to 1.5 tablespoons of mixture and roll into balls about 1.25 inches in diameter.
You should get 20–24 meatballs. Arrange them on the prepared sheet.
Bake until just cooked: Bake for 12–15 minutes, or until the centers reach 165°F (74°C) for poultry or 160°F (71°C) for beef/pork. They should be lightly browned and set.
Start the glaze: While the meatballs bake, add soy sauce, water, brown sugar, rice vinegar, honey, garlic, ginger, and mirin (if using) to a saucepan.
Bring to a gentle simmer over medium heat, stirring to dissolve the sugar.
Thicken the sauce: Stir the cornstarch slurry, then pour it into the simmering sauce. Cook for 1–2 minutes, stirring, until the glaze thickens and turns glossy. If it gets too thick, whisk in a splash of water.
Taste and adjust seasoning—add a pinch more sugar for sweetness, or vinegar for brightness.
Coat the meatballs: Transfer baked meatballs to the saucepan. Simmer for 2–3 minutes, turning gently, until every meatball is coated and sticky. The glaze should cling without dripping off.
Finish and serve: Sprinkle with sesame seeds and green onions.
Serve over rice with steamed veggies, or set out with toothpicks for appetizers. Spoon extra glaze over the top for that irresistible shine.