In a large mixing bowl, combine the ground chicken, 4 chopped green onions, breadcrumbs, garlic powder, onion powder, soy sauce, and the egg; mix gently until evenly combined.
Form the mixture into small 1-inch meatballs using your hands.
Air fryer method: arrange meatballs in a single layer in the air fryer basket and cook at 380°F for 10 minutes, or until an instant-read thermometer reads 165°F.
Baking method: place meatballs on a parchment-lined baking sheet and bake at 400°F for 20–25 minutes, or until internal temperature reaches 165°F.
Transfer cooked meatballs to a skillet, pour the 3/4 cup teriyaki sauce over them, and cook over medium-low heat until the sauce is warmed and coats the meatballs.
Garnish with the remaining chopped green onions and serve, for example over cooked rice.