In a large bowl, combine the diced cucumbers, halved cherry tomatoes, sliced red onion, and chopped parsley.
In a small bowl, whisk together the olive oil, red wine vinegar, garlic powder, salt, and pepper until well combined.
Pour the dressing over the salad mixture and toss gently to coat all the ingredients evenly.
If using, sprinkle the crumbled feta cheese on top and give the salad a light toss.
Chill the salad in the refrigerator for at least 30 minutes before serving to allow the flavors to meld.