Place lentils in a large saucepan with enough cold water to cover generously.
Add onion and bring to the boil.
Turn the heat down to medium high and simmer rapidly for about 20 minutes or until the lentils are cooked. I like them al dente like pasta but its up to you. If the lentils look dry add more water.
Drain the lentils well and place in a mixing bowl or back into the saucepan.
Stir in 3 tablespoons extra virgin olive oil. Season with soy sauce, vinegar, and a little salt and pepper if you like.