Preheat oven to 425°F (220°C) and line a sheet pan with parchment paper.
Gently toss potatoes with canola oil, garlic powder, oregano and salt until evenly coated. Spread potatoes out evenly on baking sheet and avoid overlapping.
Bake for 30 minutes, gently flipping potatoes halfway through, until golden brown all over and edges become crispy.
Meanwhile, combine topping ingredients in a small bowl, set aside.
In small bowl, whisk together ingredients for sauce, adding water 1 Tbsp at a time until the sauce is thinned and can be drizzled.
Transfer potatoes onto a serving platter. Top with cucumbers, tomato, feta and olive mixture and drizzle with yogurt sauce. Serve immediately.