In a large pot, bring the water to a boil and add the salt. Add the lentils, reduce the heat to low, and cook covered for 30 minutes. The lentils should be tender but not mushy. Take care not to overcook them or they can fall apart. While the lentils are cooking, in a medium skillet, heat 1 tablespoon of the olive oil over medium low heat. Add the garlic and cook gently for 5 to 6 minutes, or until softened and just slightly golden. Do not allow to brown. Remove from the heat and add the cumin, coriander, cayenne, and salt. Stir in the vinegar and then transfer the mixture to a large serving bowl. Drain the lentils in a colander, and immediately transfer them to the bowl. Toss together until the lentils are evenly coated with the dressing, then drizzle theremaining 4 tablespoons of olive oil over the top and toss again just to mix. Cool to room temperature, stir in the scallions and jicama, and serve immediately, or refrigerate for 1 or 2 hours, to allow the flavors to marry. Garnish with sprigs of parsley and lemon wedges.