- In a large bowl, combine the sliced cucumbers, red onion, and chopped tomatoes. 
- In a separate bowl, whisk together the white vinegar, olive oil, sugar, salt, black pepper, and dried oregano until well combined. 
- Pour the dressing over the cucumber, onion, and tomato mixture. Toss gently to coat all the vegetables evenly. 
- Cover the bowl with plastic wrap and refrigerate for at least 30 minutes to allow the flavors to meld. 
- Before serving, give the salad a gentle toss and sprinkle with fresh parsley if desired.