Place the chicken thighs in a bowl or gallon-sized Ziploc bag. In a medium mixing bowl, combine soy sauce, brown sugar, pineapple juice, chopped garlic, and minced ginger. Stir until the brown sugar dissolves. Pour the marinade over the chicken, seal the bag or cover the bowl, and refrigerate for at least 4 hours or overnight.

Remove the chicken from the marinade and set it aside. Pour the marinade into a saucepan and bring it to a simmer over medium heat. Cook for 5-10 minutes, stirring occasionally, until thickened. Preheat your grill to medium-high heat and clean and oil the grates.

Place the marinated chicken thighs on the hot grill. Baste with some of the cooked marinade. Grill for 6-7 minutes per side, or until the internal temperature reaches 165°F (75°C). Turn halfway through cooking and baste again with the marinade.

Remove the chicken from the grill and place it in a serving dish. Pour the remaining hot teriyaki marinade over the chicken. Garnish with freshly chopped parsley or green onions. Serve hot with steamed rice, grilled vegetables, or a fresh salad.