Place some the dressing in a large bowl and gently toss the watercress with the dressing, lightly shaking off excess. Remove to a serving dish. Toss the chayote with some dressing and add on top of the watercress. Repeat this process with the papaya, and then the avocado, tossing them in the remaining dressing. Season with salt and pepper and top with fried plaintain slivers.
In a glass jar with a tight-fitting lid, add all the ingredients and shake vigorously to blend. Refrigerate until ready to use.
Recipe courtesy of Wilo Benet, Pikayo Restaurant, copyright 2003