Wash and dry the cucumbers, tomatoes, and onions. Slice the cucumbers into thin rounds, dice the tomatoes into bite-sized pieces, and thinly slice the onions. Combine all vegetables in a large mixing bowl.

In a jar or bowl, whisk together the vinegar, olive oil, sugar, salt, and cracked pepper. If using a jar, secure the lid and shake until sugar is dissolved.

Pour the dressing over the vegetables and gently toss until evenly coated.

Cover and refrigerate for at least 15-20 minutes to let flavors meld.

Serve chilled or at room temperature in a large bowl or on individual plates.