1. Adjust oven rack to upper-middle position and heat oven to 425 F. Line rimmed baking sheet with aluminum foil, top with wire rack, and spray rack with oil spray.
2. Spread flour into shallow dish. In second shallow dish, whisk egg whites until foamy, then whisk in buttermilk and mustard. In third shallow dish, combine crushed Corn Flakes, oil, garlic powder, 1/2 teaspoon salt, 1/4 teaspoon pepper, poultry seasoning, and cayenne.
3. Pat chicken dry with paper towels and season with salt and pepper. Working with 1 piece at a time and coating top and sides only, dredge chicken in flour, dip in egg white mixture, then coat with Corn Flake mixture, pressing gently to adhere. Lay on prepared wire rack with uncoated side of chicken facing down.
4. Spray chicken with oil spray. Bake until crumbs are golden and chicken registers 160 degrees, about 35 minutes. Serves 4.