Wash the cucumbers thoroughly and slice them into uniform half-moon pieces about a quarter-inch thick.
Thinly slice the red onion using a mandoline or sharp knife.
Combine the cucumber slices and red onions in a large mixing bowl.
In a small jar or glass, whisk together the lemon juice and olive oil until emulsified.
Pour the dressing over the vegetables and toss gently to coat.
Fold in the feta cheese, fresh parsley, and oregano.
Allow the salad to marinate for fifteen minutes before serving to let the flavors meld.