In a bowl or zip-top bag, combine all marinade ingredients except the cornstarch slurry. Stir well.
Add chicken to the marinade and refrigerate for at least 30 minutes or up to 8 hours.
Remove chicken from marinade and pat dry. Reserve the marinade for the sauce.
Heat oil in a skillet or grill pan over medium-high heat. Cook chicken for 6–7 minutes per side, or until cooked through and nicely browned.
While chicken cooks, pour reserved marinade into a small saucepan. Bring to a simmer, then stir in the cornstarch slurry. Cook 1–2 minutes until thickened.
Slice chicken and drizzle with thickened teriyaki sauce. Garnish with sesame seeds and green onions.
Serve over steamed rice or with stir-fried vegetables.