Wash cucumbers and cherry tomatoes under cold water. Thinly slice cucumbers, halve tomatoes, and slice red onion. Chop parsley.

In a medium bowl, whisk together olive oil, red wine vinegar, salt, black pepper, and oregano until smooth.

In a large mixing bowl, combine cucumbers, cherry tomatoes, red onion, and parsley. Pour dressing over and toss gently.

Cover and refrigerate for at least 30 minutes to chill before serving.