Set aside the chicken to rest and cool.
In a large bowl combine the watermelon, jalapeño, tomatoes, capers, avocado, olive oil, salt, pepper, and mint leaves. Gently stir to combine. Taste and adjust seasonings to your liking.
Slice the chicken breasts. Set 3 to 4 pieces of the chicken on a plate, then top with the watermelon salad. Finish with a sprinkle of flake salt for a bit of crunch.