Rinse lentils well, drain. Place in a pot and cover with a 3-4 inches of water, bring to a boil, reduce to simmer. Check lentils for doneness after 15 minutes, but they should take about 20 minutes in total. You will know they are cooked if they still retain a slight tooth – al dente! Overcooking the lentils is the death of this dish. Be careful!
While the lentils are simmering, make the dressing by placing all ingredients in a jar with a tight fitting lid and shake vigorously to combine.
Finely dice red onion - the salad is best if all the ingredients are about the same size. If using raisins, chop them roughly to make them a bit smaller, and do the same with the capers if they are large.
When the lentils are cooked, remove from heat, drain and place under cold running water to stop the cooking process. Once cooled slightly but still a little warm, place lentils in a large serving bowl and toss with dressing. Add other onion, capers, and currants. If using other add-ins such as herbs, greens, or cheese, wait until just before serving. Otherwise, this salad can hang out in the fridge for a couple days.