Preheat oven to 425°F and line a baking sheet with parchment paper.
In a bowl, stir together the Greek yogurt, mayo, garlic powder, lemon juice, dill, Dijon mustard, and chopped cucumber. Set this aside in the fridge so the flavors can blend.
Cut the potatoes into bite-sized pieces. Toss them with the avocado oil and a bit of salt.
Place potatoes on the baking sheet. Roast in the oven at 425°F for 35-40 minutes until they are golden and crispy.
Spread the dressing in a thick layer on a plate or platter. Pile the hot potatoes right on top and serve immediately.