Chicken: Rinse and pat dry the chicken breasts with paper towel. Using a sharp knife, split the chicken breasts into half to get a total of 4 thin slices. Alternatively, cover them with a layer of baking parchment or clingfilm and pound them with a mallet/rolling pin until they are of even thickness.
Combine the chicken with the rest of the ingredients and leave it to marinade for a couple of hours, or overnight if desired.
Salsa: While the chicken is marinating, combine the mango, onion, tomato and juice of 1 lime together. Taste and add more lime juice if desired. Stir in cilantro leaves. Cover and refrigerate for at least 1 hour for the flavours to mingle and get friendly.
Back to the chicken: Grill or pan-fry the chicken until cooked (discard the marinade). Serve with salsa and rice.