Huli Huli Chicken

Make the Marinade:
In a mixing bowl, whisk together pineapple juice, soy sauce, brown sugar, ketchup, rice vinegar, garlic, ginger, and black pepper.
Set aside 1/2 cup of the marinade for basting.
Marinate the Chicken:
Place chicken thighs in a resealable plastic bag or a shallow dish. Pour the marinade over the chicken, ensuring even coating.
Seal the bag or cover the dish, and refrigerate for at least 2 hours, or overnight for enhanced flavor.
Prepare the Grill:
Preheat your grill to medium heat. Remove the chicken from the marinade and discard the used marinade.
Thicken the Marinade (Optional):
For a thicker basting sauce, pour the reserved marinade into a small saucepan.
Bring to a simmer, mix cornstarch with a bit of water to make a slurry, and stir it into the simmering marinade until thickened. Set aside.
Grill the Chicken:
Place the chicken on the grill and cook for 5-7 minutes per side, or until fully cooked (internal temperature of 165°F/74°C).
In the last few minutes of cooking, brush the chicken with the reserved marinade.
Rest and Slice:
Let the chicken rest for a few minutes after grilling to retain its juices. Slice as desired.
Serve and Garnish:
Plate the chicken hot, garnished with sliced green onions and sesame seeds if desired.