Preheat oven to 425°. Peel and cut potatoes lengthwise into 1/2-in.-thick slices; cut slices into 1/2-in.-thick sticks., In a large bowl, toss potatoes with oil and pepper. Transfer to a 15x10x1-in. baking pan coated with cooking spray. Bake, uncovered, 25-30 minutes or until golden brown and crisp, stirring once. , Meanwhile, in a shallow bowl, mix flour and pepper. In another shallow bowl, whisk egg with water. In a third bowl, toss cornflakes with cheese and cayenne. Dip fish in flour mixture to coat both sides; shake off excess. Dip in egg mixture, then in cornflake mixture, patting to help coating adhere. , Place on a baking sheet coated with cooking spray. Bake 10-12 minutes or until fish just begins to flake easily with a fork. Serve with potatoes and, if desired, tartar sauce.