Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper for easy cleanup.
In a large mixing bowl, combine the ground turkey (or chicken), breadcrumbs, chopped green onions, cilantro, beaten egg, garlic powder, ginger powder, salt, and pepper. Mix until everything is well incorporated.
Roll the mixture into 1-inch meatballs and place them on the prepared baking sheet.
Bake the meatballs in the preheated oven for 18-20 minutes or until fully cooked through (internal temperature of 165°F/75°C).
While the meatballs are baking, prepare the teriyaki sauce. In a saucepan, combine the pineapple juice, soy sauce, brown sugar, and cornstarch (if using) over medium heat.
Stir the mixture until the brown sugar dissolves and bring it to a simmer. Let it cook for about 5-7 minutes until it thickens slightly.
Once the meatballs are done, remove them from the oven and transfer to the saucepan with the teriyaki sauce. Toss to coat the meatballs evenly in the sauce.
Allow the meatballs to simmer for an additional 2-3 minutes in the sauce to soak up the flavors.
Serve the meatballs in a bowl or on a platter, garnished with sesame seeds and additional chopped green onions if desired.