Add cucumbers, tomatoes, and onion to a large bowl. If you don't like the skin of cucumbers, feel free to peel them prior to slicing.
In a medium bowl, stir together the remaining ingredients to create the dressing. Pour over the cucumber mixture and fold gently to combine. Place salad in a serving bowl, sprinkle with a bit more black pepper, and serve immediately.
This can be prepared many hours in advance, or even the day prior to serving. Just store the cucumber mixture and dressing mixture in separate containers in the refrigerator, combining them just prior to serving.