In a medium bowl, combine the soy sauce, honey, olive oil, minced garlic, ground ginger, black pepper, and red pepper flakes (if using). Whisk until well blended.

Place the chicken breasts in a large resealable plastic bag or shallow dish and pour the marinade over the chicken. Seal the bag or cover the dish and refrigerate for at least 1 hour, or up to 4 hours for more flavor.

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

Grill the chicken for about 6-7 minutes on each side, or until the internal temperature reaches 165°F and the chicken is cooked through.

While the chicken is grilling, toss the diced pineapple and mango in a bowl. Once the chicken is done, remove it from the grill and let it rest for 5 minutes.

Slice the chicken and serve it topped with the fresh mango and pineapple mixture. Garnish with chopped cilantro.