In a small bowl, soak the onion slices in icy cold water for 15 minutes. Remove from the water and pat dry. In a large bowl, add the onions, cucumbers and tomatoes and toss to combine.
In a small bowl, whisk together the lemon juice, olive oil and salt and pepper, to taste. Pour over the salad and serve immediately.
Feel free to add some nice salty feta cheese to this dish to make a nice light lunch. You will be eating this salad all summer long and dreaming of it all winter. You can also chop all the parts the night before so when it comes time to serve all you have to do is mix it together.