In a medium bowl, combine pineapple juice, soy sauce, brown sugar, ketchup, chicken broth, grated ginger, and minced garlic. Stir until the sugar dissolves. Set aside 1 cup of the sauce for basting the chicken later.
Place the chicken thighs in a large ziplock bag and pour the marinade over them. Seal the bag and refrigerate for at least 3 hours, or overnight for deeper flavor.
Preheat the grill to medium heat. Grill the marinated chicken, covered, for 6-8 minutes per side, or until the chicken is fully cooked and no longer pink in the center. During the last 5 minutes of grilling, occasionally baste the chicken with the reserved marinade.
Once cooked, remove from the grill and garnish with sliced green onions, if desired. Serve hot and enjoy!