In a large bowl add the ground chicken, green onion, eggs, 1/3 cup hoisin sauce, 2 tablespoons sesame oil, and panko. Use your hand to gently combine the ingredients. Shape into 1-1/2 inch balls and place on a non-stick baking sheet. Bake at 350°F for 30 minutes or until meatballs are done inside. Meanwhile, in a small saucepan add 2 tablespoons sesame oil, 2/3 cups hoisin sauce, and rice vinegar, stir to combine and heat through. Once the meatballs are done, pour this sauce over the meatballs and serve.