01 - In a bowl or resealable bag, whisk together soy sauce, mirin, honey, rice vinegar, garlic, ginger, and sesame oil. Add chicken and turn to coat. Cover and refrigerate for 30 minutes to 4 hours.
02 - Preheat grill to medium-high heat. Lightly oil the grates.
03 - Remove chicken from marinade and shake off excess (reserve marinade for glaze).
04 - Grill chicken for 6-8 minutes per side, or until internal temperature reaches 165°F (74°C) and grill marks appear.
05 - Pour reserved marinade into a small saucepan. Bring to a boil for 2 minutes. Stir in cornstarch slurry (if using) and simmer until thickened. Brush over grilled chicken before serving.
06 - Slice chicken and serve over rice or with vegetables. Garnish with sesame seeds and green onions if desired.