01 - Combine ground chicken, egg, panko, green onions, soy sauce, mirin, grated ginger, garlic, salt, and black pepper in a large bowl. Mix until just combined, being careful not to overwork the mixture.
02 - Moisten hands with water and form the mixture into 16 evenly sized meatballs, rolling gently to maintain tender texture.
03 - Heat vegetable oil in a large nonstick skillet over medium heat. Add meatballs and cook for 8–10 minutes, turning occasionally, until browned on all sides and cooked through. Transfer to a plate and set aside.
04 - Wipe the skillet clean. In a small bowl, whisk together soy sauce, mirin, sake, sugar, cornstarch, and water until smooth and the cornstarch is fully dissolved.
05 - Pour the sauce mixture into the skillet and bring to a simmer over medium heat. Stir constantly until the sauce thickens and coats the back of a spoon, about 2 minutes.
06 - Return the cooked meatballs to the skillet and gently toss to coat evenly in the teriyaki sauce. Simmer for 2–3 minutes, allowing the glaze to adhere and the flavors to meld.
07 - Plate the glazed meatballs over steamed rice if desired. Garnish generously with sliced green onions and toasted sesame seeds. Serve immediately while hot.