Step 1: In a large bowl, whisk together the pineapple juice, low-sodium soy sauce, brown sugar, ketchup, rice vinegar, grated fresh ginger, minced garlic, sesame oil, and red pepper flakes (if using). This is your huli huli marinade.
Step 2: Place the chicken thighs in a large resealable bag or a non-reactive dish. Pour the marinade over the chicken, ensuring all pieces are well coated. Seal the bag or cover the dish, and refrigerate for at least 4 hours, or preferably overnight, to allow the flavors to meld and tenderize the chicken.
Step 3: When ready to cook, remove the chicken from the marinade. Reserve about 1/2 cup of the marinade for basting during cooking. Discard any remaining marinade that came into contact with raw chicken.
Step 4: Preheat your grill to medium-high heat (375-400°F or 190-200°C) or your oven to 375°F (190°C). Lightly oil your grill grates or line a baking sheet with foil.
Step 5: For grilling: Place chicken on the preheated grill. Grill for 6-8 minutes per side, basting frequently with the reserved marinade during the last 10 minutes of cooking, until the chicken is cooked through and has a beautiful, caramelized glaze. An instant-read thermometer inserted into the thickest part should read 165°F (74°C).
Step 6: For oven baking: Arrange chicken on the prepared baking sheet. Bake for 25-35 minutes, flipping halfway through. During the last 10-15 minutes, baste frequently with the reserved marinade until the chicken reaches 165°F (74°C) and is golden brown and glazed.
Step 7: Once cooked, remove the huli huli chicken from the grill or oven and let it rest for 5-10 minutes before serving. This allows the juices to redistribute, ensuring tender and juicy results.
Step 8: Serve hot with your favorite sides like rice, macaroni salad, or grilled pineapple. Enjoy your taste of Hawaii!