In a mixing bowl, combine the chopped mango, lime juice, agave syrup, olive oil, chopped garlic, cumin, sea salt, black pepper, and crushed red pepper flakes. Stir until well incorporated.
Place the chicken breasts in a large resealable bag or shallow dish, pour the marinade over the chicken, and ensure it is evenly coated. Seal the bag or cover the dish and let it marinate in the refrigerator for 30 minutes to 2 hours.
Preheat your grill to a medium-high setting.
Remove the chicken from the marinade and discard the leftover marinade.
Grill the chicken for about 6-7 minutes on each side, or until it reaches an internal temperature of 165°F.
Transfer the chicken to a plate and allow it to rest for 5 minutes before slicing it into strips.
Arrange the sliced chicken on a platter, garnishing it with additional chopped mango and a sprinkle of fresh cilantro.