Toss the jicama in a colander with the lemon juice and let sit for 15 minutes. Using your hands, squeeze as much water as you possibly can out of the jicama, a handful at a time. Spread on a doubled layer of paper towels and blot with more paper towels. In a large bowl, toss the jicama with the onion, egg, flour, salt, and chili. Toss well to be sure the chile is evenly distributed in the mixture. Grate the potato into the bowl on the largest hole of the grater and toss again.

In a large cast-iron skillet, heat I tablespoon of the oil over medium-high heat until very hot. Form the mixture into 2 1/2-inch patties and saute them in batches, turning with a metal spatula when brown on one side, until crisp and brown. Add more oil to the skillet as necessary and keep the pancakes warm on a paper towel-lined baking sheet in a warm oven while you finish cooking the rest. Serve warm.

Note: remove the outer brown layer of skin from the jicama. Shred on the largest hole of a grater.