1. Preheat the oven to 425 degrees. Line two rimmed baking sheets with foil and mist with cooking spray. Bring a small pot of water to a boil. Add the onion and boil 1 minute. Drain in a sieve and let cool.
2. In a bowl, combine onion with the turkey, egg white, bread crumbs, sesame oil, soy sauce and garlic powder. Season with the black pepper and stir until combined.
3. Scoop out slightly rounded teaspoons of the turkey mixture, roll into 3/4-inch meatballs and place on prepared baking sheets. (Dampen hands before handling meatballs, as mixture will be sticky.)
4. Whisk together the hoisin and sriracha in a small bowl. Spoon about 1/4 teaspoon of the glaze over each meatball. Place baking sheets in oven and bake until meatballs are just cooked through, 6 to 7 minutes.
5. Remove from oven. Preheat broiler; broil meatballs, watching carefully, until glaze is sizzling, 1 to 2 minutes. Drizzle orange juice over meatballs and transfer to a platter. Garnish with cilantro if desired, skewer with toothpicks and serve.