Preheat Oven: Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
Make the Meatball Mixture: In a large bowl, combine ground turkey, panko breadcrumbs, egg, green onions, garlic, ginger, sesame oil, salt, and pepper. Mix gently until just combined.
Form the Meatballs: Using a spoon or your hands, roll the mixture into 1 ¼-inch meatballs and place them on the prepared baking sheet.
Bake: Bake for 15-18 minutes, or until the meatballs are golden brown and the internal temperature reaches 165°F (75°C).
Prepare the Teriyaki Sauce: While the meatballs are baking, combine soy sauce, brown sugar, hoisin sauce, sesame oil, garlic, ginger, and water in a small saucepan. Heat over medium until simmering.
Thicken the Sauce: Stir in the cornstarch slurry (cornstarch mixed with water) and let the sauce simmer for 2-3 minutes until thickened.
Coat the Meatballs: Once baked, toss the meatballs in the teriyaki sauce until evenly coated.
Serve: Garnish with sesame seeds and additional green onions. Serve hot over rice, noodles, or as an appetizer.