Preheat oven to 425. Line two baking sheets with aluminum foil and place a wire baking rack on top (I used two metal cooling racks).Lightly mist the racks with cooking spray. Combine the Parmesan, bread crumbs, pepper and garlic powder in a shallow dish and mix together. In a small bowl, beat the two egg whites. Dip each zucchini round in the egg whites to coat both sides and then press each side of the round into the bread crumb/Parmesan mixture. Place the coated round on the wire rack on the baking sheet. Repeat with remaining zucchini rounds. Bake for 30-35 minutes until the Parmesan and bread crumb coating is browned and crisp. Serve immediately.