To remove some of the bitterness/spiciness from the onions, place the onion slices in a bowl, sprinkle about ½ tablespoon of salt over the onions. Rub the salt in and then cover with water for a few minutes. Then drain and rinse the onions well.Place the sliced cucumbers, sliced onions, lime juice, chopped cilantro, and olive oil in a bowl.Mix well, taste and add salt as needed.Serve immediately or let rest refrigerated for at least 30 minutes before serving.