In a medium bowl, whisk together the sour cream (or Greek yogurt), mayonnaise, Dijon mustard, and pickle juice until smooth. Add garlic powder, dried onion, dried parsley, and a pinch of salt and pepper for flavor. Taste and adjust the pickle juice according to your desired tanginess, then set aside the dressing.

Slice the Persian cucumbers into thin rounds. If using optional pickles, dice them and slice the red onion. In a large mixing bowl, combine the cucumbers, optional pickles, and sliced red onion, tossing gently to mix.

Pour the prepared dressing over the cucumber mixture in the large bowl. Gently toss everything together until all cucumber slices are evenly coated.

Cover the bowl and refrigerate the salad for at least 15 minutes to allow flavors to meld before serving.