Thoroughly wash and dry the cucumbers, cherry tomatoes, and onion. Slice the cucumbers into thin rounds, cut the cherry tomatoes in half, and slice the onion into thin half-moons.

In a medium mixing bowl, combine the olive oil and white wine vinegar. Add the salt, black pepper, dried parsley, and crushed red pepper flakes. Whisk together for about 30 seconds until well-emulsified.

In a large mixing bowl or jar, add the sliced cucumbers, halved cherry tomatoes, and onion. Pour the marinade over the vegetables and gently toss together to coat evenly.

Cover the bowl with plastic wrap or seal the jar and refrigerate for at least 1 hour, but overnight is ideal for better flavor.

After marination, gently stir the salad to redistribute the marinade and serve as a fresh side dish or snack.