Preheat oven to 425°F. In a large bowl, combine the ground turkey, breadcrumbs, green onion, garlic, ginger, egg, soy sauce, sesame oil and red pepper flakes. Squish the mixture with your hands until mixed. The mixture should be fairly wet.
Use wet hands or an ice cream scoop to shape the meatballs to desired size, usually golf ball size. Put some parchment paper on a baking sheet and place meatballs in single layer. Bake for about 15 to 20 minutes or until meatballs start to brown on top.
While meatballs are baking, make the glaze. In a large sauce pan, add the hoisin sauce, soy sauce, rice wine vinegar, sesame oil, garlic and ginger and heat over medium heat for 5 minutes. Whisk together the water and cornstarch in a measuring cup and add to the sauce. Cook for another 5 minutes until thickened.
Add the meatballs, tossing to coat. Top with sesame seeds and green onions.
Don’t over-mix! Over-mixing the meatballs will make them tough.
Use an ice cream scoop to make the meatballs equal in size so they all cook the same.
Use cold ingredients to keep the fat from melting before transferring to the oven.
Remove the sauce from the heat as soon as it is thickened, otherwise it will get too gloopy.