In a mixing bowl, combine pineapple juice, soy sauce, brown sugar, minced ginger, garlic, vegetable oil, and black pepper. Whisk until the sugar dissolves.

Place the chicken thighs in a resealable plastic bag or shallow dish. Pour the marinade over the chicken, ensuring they are well-coated. Seal the bag or cover the dish and refrigerate for at least 15 minutes, or up to 2 hours for more flavor.

Preheat your grill to medium-high heat. Lightly grease the grates with cooking spray or oil to prevent sticking.

Remove the chicken from the marinade, allowing excess marinade to drip off. Place the chicken on the hot grill. Cook for about 5-7 minutes on each side, or until the chicken reaches an internal temperature of 165°F and has beautiful grill marks.

Use a brush to apply some of the reserved marinade on the chicken while grilling for added flavor, but avoid cross-contamination by not using the same brush for raw chicken.

Once cooked, transfer the chicken to a plate. Sprinkle with sliced green onions and sesame seeds before serving.