In a mixing bowl, combine soy sauce, brown sugar, pineapple juice, minced garlic, grated ginger, and black pepper to create the marinade.

Place the chicken breasts in the marinade, ensuring they are fully coated. Cover and refrigerate for at least 30 minutes, or up to 4 hours for more flavor.

In a saucepan, combine pineapple chunks, brown sugar, cornstarch, water, and soy sauce.

Cook over medium heat, stirring constantly, until the sauce thickens and bubbles. Remove from heat and set aside.

Preheat the grill to medium-high heat. Remove chicken from the marinade and discard the marinade.

Grill the chicken for about 6-7 minutes on each side, or until fully cooked and internal temperature reaches 165°F (75°C).

Once the chicken is cooked, remove from the grill and let rest for a few minutes.

Serve the grilled chicken topped with the pineapple sauce. Enjoy!