Step 1 Using a sharp heavy knife, cut off the top and bottom of the jicama and peel it, cutting away the rounded edges to form a rough cube. Cut the jicama in slices between one-eighth and one-fourth-inch thick. Stack some of the slices and cut the same thickness into sticks. Collect the sticks into a mixing bowl and repeat with the rest of the jicama.
Step 2 Add the onion, garlic and jalapeno to the jicama. Stir together the oil, lime juice and salt and pour over everything. Toss to coat lightly. Taste and adjust the seasoning. (Recipe can be prepared up to this point several hours in advance and refrigerated tightly covered.)
Step 3Before serving, transfer the salad to a clean bowl, draining any excess dressing, and sprinkle with cilantro leaves.