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—do not overwork the mixture.
02 - Wet your hands to prevent sticking and form the mixture into 16 evenly sized meatballs, rolling gently between your palms.
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. Remove from skillet and set aside.
04 - Wipe the skillet clean. In a small bowl, whisk together soy sauce, mirin, sake, sugar, cornstarch, and water until cornstarch is fully dissolved.
05 - Pour the sauce mixture into the skillet and bring to a simmer over medium heat, stirring constantly until thickened, about 2 minutes.
06 - Return the cooked meatballs to the skillet and gently toss to coat them evenly in the sauce. Simmer for 2–3 minutes, allowing the glaze to adhere to the meatballs.
07 - Serve hot over steamed rice if desired, garnished with sliced green onions and toasted sesame seeds.