Prepare the Chicken:
Trim any excess fat from the chicken. If using breasts, pound them to an even thickness for even cooking.
Make the Teriyaki Sauce:
In a small bowl, whisk together soy sauce, mirin, sugar, sake (if using), ginger, and garlic.
Cook the Chicken:
Heat the vegetable oil in a large skillet over medium-high heat. Add the chicken and cook for 4–5 minutes per side, or until golden brown and fully cooked. Remove from the skillet and set aside.
Create the Glaze:
Lower the heat to medium. Pour the teriyaki sauce mixture into the skillet, scraping up any browned bits. Let it simmer for 2–3 minutes until slightly thickened.
Thicken the Sauce (Optional):
If a thicker glaze is desired, mix the cornstarch with water to create a slurry. Stir it into the sauce and cook for another 1–2 minutes until the sauce thickens.
Coat the Chicken:
Return the chicken to the skillet, turning to coat it evenly with the teriyaki sauce.
Serve:
Slice the chicken into strips and serve over rice or noodles. Garnish with sesame seeds and green onions.