Toss the jicama, mango, and jalapenos. Add as many pickled red onion slices as you like (I use about a third of a cup). Spoon the juice from the jar over the slaw, or enough to flavor everything but not drench it with excess liquid (you can always add more right before serving). Refrigerate it for at least 30 minutes, or until ready to serve. Sprinkle on cilantro just before serving.