Preheat oven to 400º F. Line a large baking sheet with parchment paper and set aside.
In a large bowl, combine the ground chicken, panko, egg, green onions, garlic, salt, and pepper. Stir until well combined.
Using a medium cookie scoop or a spoon, scoop and roll the mixture into 2-tablespoon balls and place them on the prepared baking sheet. You can wear gloves or lightly spray your hands with nonstick cooking spray.
Bake for 15 to 20 minutes or until browned and cooked through. Check early so you don’t overcook and dry out the meatballs. Remove from the oven.
While the meatballs are baking, make the sauce. In a small mixing bowl, whisk together soy sauce, brown sugar, vinegar, sesame oil, fresh ginger, garlic, and cornstarch.
Pour the sauce in a large skillet. Heat over medium heat and bring to a boil. Reduce to low and simmer for about 5 minutes, stirring occasionally, or until the sauce thickens. Turn off the heat and add the warm meatballs. Stir until meatballs are well coated in the sauce.
Garnish with sesame seeds and sliced green onions. Serve with rice, if desired.