In a large bowl, combine the turkey, onion, breadcrumbs, egg, sesame oil and soy sauce, mixing with your hands just until combined.
Shape the mixture into 1-inch balls and bake on a cookie sheet in the oven (at 375˚F for about 20 minutes), or in a drizzle of oil in a skillet on the stovetop until cooked through.
In a small bowl, whisk together the hoisin sauce, rice vinegar, soy sauce, garlic and ginger and toss with the warm meatballs.
Serve garnished with sesame seeds and green onion.
