Preheat the oven to 350 degrees. Add the ground turkey, egg, bread crumbs, soy sauce, and some freshly ground pepper to a large bowl. Peel the ginger with a vegetable peeler or by scraping the skin off with the side of a spoon. Use a small holed cheese grater to grate about two inches of the ginger straight into the bowl. Thinly slice 2-3 of the green onions and add to the bowl (save the rest for later).
Mix the ingredients in the bowl thoroughly. Shape the meat mixture into meatballs about the size of pingpong balls. You should get 25-30 meatballs, depending on the size. Arrange the meatballs on a baking sheet covered in foil and bake in the preheated oven for 25 minutes.
While the meatballs are baking, make the sriracha glaze. In a small pot combine the soy sauce, rice vinegar, brown sugar, sriracha and 1/4 cup of the water. Heat and stir the mixture over medium heat until the brown sugar is dissolved. In a small bowl, stir together the remaining 1/4 cup of water with the cornstarch. Pour the cornstarch slurry into the pot with the glaze. Stir to combine. Allow the mixture to come up to a simmer, at which point the glaze will thicken and become glossy.
After the meatballs are finished baking, transfer them to a large bowl and pour the glaze over top. Carefully toss the meatballs to coat in the glaze. Serve hot topped with the remaining sliced green onions.