Cut fillets diagonally into 1-inch-wide strips. Combine fish strips and buttermilk in a bowl, stirring gently to coat strips.
Tear bread into large pieces and place in container of a blender; process until crumbly. Spread 1/2 cup crumbs on a baking sheet and bake at 400° for 3 to 5 minutes or until toasted.
Combine breadcrumbs, cornmeal, and pepper in a heavy-duty, zip-top plastic bag. Add buttermilk-coated fish strips; seal bag, and gently turn bag to coat fish strips.
Place fish strips on a baking sheet coated with cooking spray; sprinkle with salt. Bake at 425° for 25 minutes or until fish is crisp and flakes easily when tested with a fork. Serve with malt vinegar, if desired.