Quick and easy to prepare, salsa criolla is the perfect accompaniment to many dishes. The lime juice is what makes this onion salsa/relish special. It adds a bright flavor that sweetens the onions and livens up everything else on the plate. For authenticity's sake, it's important to cut the onions "a la pluma," or like feathers. Slice them into to very thin half moons, retaining the curve of the onion, so that they look like little curls on the plate. In Peru, this salsa is made with ají peppers, but jalapeños make a reasonable substitute. Some people also add tomatoes and/or garlic.