Preheat oven to 400 degrees Fahrenheit.
Line a large baking sheet with parchment paper or foil. Spread diced potatoes on the tray, drizzle with olive oil, season with salt and pepper, and toss.
Bake 45–50 minutes until golden and fork-tender, flipping twice for even cooking. Let cool before mixing. Slightly warm is fine, but fully cooled gives the best texture.
In a large bowl, combine mayonnaise, sour cream, ranch dressing, and parsley. Cover and refrigerate 30 minutes to let flavors blend.
Cook bacon on a dry nonstick pan over medium heat until crispy (or to the desired liking). Set aside paper towels to drain the excess fat.
Add potatoes, red onion, bacon, and cheese to the dressing (add cucumbers last). Gently toss and chill at least 30 minutes. Garnish with parsley, green onions, and extra crispy bacon.