To a large bowl, add the melted butter, olive oil, garlic powder, onion powder, smoked paprika, salt, some black pepper and 3 tablespoons of the Parmesan, then mix together. Add the potato slices and toss to coat.
Coat 2 large baking sheets with cooking spray. Spread the potato slices in one layer on the prepared baking sheets. Sprinkle the potatoes with the remaining 1 tablespoon Parmesan and bake until the potatoes are tender, crisp and golden, 15 to 20 minutes. Transfer them to a serving dish and sprinkle with the parsley.