1. Adjust oven racks to center and lower third of oven. Heat oven to 475 degrees F. Lightly coat two large cookie sheets with olive oil cooking spray. Pat sliced potatoes with paper towels. Toss potatoes with oil, salt and pepper in a large bowl until well coated. Divide potatoes and spread in a single layer on prepared sheets. Bake potatoes 25 to 30 minutes, switching pans once halfway through, until lightly browned. Cover loosely with foil to keep warm.Make Fish::
2. Reduce oven temperature to 200 degrees F. Cut each fillet crosswise in half. Combine buttermilk and red pepper in pie plate. Combine cornflake crumbs and chopped parsley on a sheet of waxed paper. Dip each piece of fish in buttermilk mixture and coat with crumbs. Place on cookie sheet or large plate.
3. Heat a large nonstick skillet over medium-high heat 1 minute. Lightly coat pan with olive oil cooking spray. Add half of the fish; cook 4 to 5 minutes, turning once halfway through, until fish is crisp and golden, and opaque in center when tested with a small knife. Transfer to cookie sheet and place in oven to keep warm. Repeat process with cooking spray and remaining fish.
4. Divide potatoes and fish among 4 serving plates; serve with malt vinegar and garnish with parsley sprigs, if desired.