1. Pat the boneless skinless chicken thighs dry with paper towels and trim any large pieces of visible fat so the marinade can cling well and the chicken browns nicely.

2. In a medium bowl, whisk together the pineapple juice, soy sauce, brown sugar, rice vinegar, sesame or neutral oil, minced garlic, grated fresh ginger, and ketchup or tomato paste if using, then taste and adjust the seasoning.

3. Place the chicken thighs in a large zip-top bag or shallow dish, pour the marinade over the top, and turn the pieces so every side is coated evenly.

4. Cover and refrigerate the chicken for at least 2 hours and up to 24 hours, flipping the bag or turning the pieces once or twice while they marinate.

5. When you’re ready to cook, remove the chicken from the fridge and let it sit at room temperature for about 15 minutes while you preheat the grill to medium-high heat.

6. Clean and oil the grill grates, then lift the chicken from the marinade, letting excess drip off, and reserve the remaining marinade in a small bowl.

7. Arrange the chicken on the hot grill and cook for 5–7 minutes per side, or until the internal temperature reaches 165°F (74°C) and the outside has dark grill marks.

8. While the chicken cooks, pour the reserved marinade into a small saucepan, bring it to a boil over medium heat, and let it bubble for a few minutes.

9. Stir together the cornstarch and water in a small bowl to make a slurry, whisk it into the boiling marinade, and simmer until the sauce thickens into a glossy teriyaki glaze.

10. Brush the thickened glaze over the chicken during the last minute or two of grilling, then transfer the cooked pieces to a serving platter.

11. Drizzle any extra glaze over the top, then garnish the Hawaiian Teriyaki Chicken with sliced green onions, toasted sesame seeds, and a pinch of crushed red pepper flakes if you like a little heat.

12. Serve hot with your favorite sides, such as rice, grilled vegetables, or a fresh salad.