In a mixing bowl, combine soy sauce, mirin, honey, minced garlic, grated ginger, and sesame oil. Whisk until well combined to create the teriyaki marinade.
Place the chicken breasts in a shallow dish or resealable plastic bag and pour the marinade over them, ensuring they are fully coated. Marinate in the refrigerator for at least 30 minutes, or up to 4 hours for maximum flavor.
Preheat your grill, skillet, or oven to medium-high heat. If using a grill or skillet, lightly oil the cooking surface to prevent sticking.
Remove the chicken breasts from the marinade, shaking off any excess, and place them on the preheated cooking surface. Discard the remaining marinade.
Cook the chicken for 6-8 minutes per side, or until the internal temperature reaches 165°F (75°C) and the chicken is cooked through, basting occasionally with additional marinade.
Once cooked, transfer the chicken to a cutting board and let it rest for a few minutes before slicing.
If desired, thicken the remaining marinade with cornstarch by whisking together in a small saucepan over medium heat until thickened, then drizzle over the sliced chicken.
Garnish with sesame seeds and sliced green onions, if desired, and serve hot with steamed rice or vegetables.