Preheat oven to 475°F. Coat a large baking sheet with cooking spray. Combine flours, cornmeal, salt and pepper in a large sealable plastic bag. Dip zucchini in egg white, shake in the bag to coat, and arrange, not touching, on the baking sheet. Coat all exposed sides with cooking spray. Bake on the center rack for 7 minutes. Turn the zucchini and coat any floury spots with cooking spray. Continue to bake until golden and just tender, about 5 minutes more. Serve hot.