
Place the onion in a small bowl of ice water and let it soak for at least 5 minutes to tame the flavor.
In the meantime, combine the cucumber, cherry tomatoes, optional feta, and herbs in a medium serving bowl. Once the onions are drained, add them to the bowl. Drizzle the dressing over the salad and toss to combine.
For best flavor, let the salad rest for at least 10 minutes before serving. This salad keeps well in the refrigerator, covered, for up to 4 days.