Position racks in upper and lower third of oven; preheat to 425 degrees F. Coat a large baking sheet with cooking spray. Set a wire rack on another large baking sheet; coat with cooking spray.

Place potatoes in a colander. Thoroughly rinse with cold water, then pat dry completely with paper towels. Toss the potatoes, oil and 3/4 teaspoon Cajun (or Creole) seasoning in a large bowl. Spread on the baking sheet without the rack. Bake on the lower oven rack, turning every 10 minutes, until tender and golden, 30 to 35 minutes.

Meanwhile, coarsely grind cornflakes in a food processor or blender or crush in a sealable plastic bag. Transfer to a shallow dish. Place flour, the remaining 3/4 teaspoon Cajun (or Creole) seasoning and salt in another shallow dish and egg whites in a third shallow dish. Dredge fish in the flour mixture, dip it in egg white and then coat all sides with the ground cornflakes. Place on the prepared wire rack. Coat both sides of the breaded fish with cooking spray.

Bake the fish on the upper oven rack until opaque in the center and the breading is golden brown and crisp, about 20 minutes.

Note: Overfishing and trawling have drastically reduced the number of cod in the Atlantic Ocean and destroyed its sea floor. A better choice is Pacific cod (a.k.a. Alaska cod); it is more sustainably fished and has a larger, more stable population, according to Monterey Bay Aquarium Seafood Watch (mbayaq.org/cr/seafoodwatch.asp).