If you are using frozen mango or pineapple, prep that fruit first. If not, cut the watermelon first.
SCRUB the outside of the watermelon, cucumber, jicama, and mango (if using fresh) with a vegetable scrubber under cool running water.
SLICE the watermelon in half. Lay one half face down with the red side on the cutting board. Start at one end and cut 1-inch-thick slices. Then, cut the rind off each watermelon slice. Finally, chop the watermelon into cubes.
DRAIN the watermelon. Measure out the watermelon for the salad and place it in a colander over a bowl to catch the drips. Refrigerate as it drains (optional).
PREP the mango and pineapple. If you are using frozen fruit, measure the fruit and run it under warm water for about 20 seconds. Then leave it in a colander to drain. If you are using canned fruit, open the can, measure the fruit, and let it drain.
PEEL and DICE the jicama. Dice the cucumber. (Optional: Peel the cucumber before dicing it. I prefer to leave it unpeeled.) Sprinkle the cucumber with a pinch of salt and leave it to drain on a paper towel. Pat it dry before adding it to the salad.
CHOP the fresh cilantro.
JUICE the limes.
ADD the watermelon, mango, pineapple, cucumber, and jicama to a large bowl with half of the cilantro.
POUR in the lime juice.
USE as much chili seasoning as you like. Start with 2 teaspoons and go from there. Be sure to taste as you go.
COVER and refrigerate for 10-15 minutes to give the flavors time to meld.
GARNISH with the remaining cilantro and serve.