Cook's Illustrated (they're the ones who test 90 versions of a recipe to find the best one - also known as America's Test Kitchen on PBS) did oven fried chicken a few years ago and found the best topping to make it crunchy was melba toast. Here's the recipe - I'm sure it would work fine with fish.
Golden, crunchy, and on the table in under an hour
For those who like breast meat, use a whole cut-up chicken instead of drumsticks and thighs. Be careful not to overcrush the Melba toast; crumbs that are too fine will leave the chicken wanting in crunchiness. If you own a spray bottle for oil, skip the step of tossing the Melba toast crumbs in oil. Instead, once the chicken is coated with crumbs, spray the pieces evenly with oil.
1/4 cup vegetable oil
1 box (about 5 ounces) plain Melba toast, placed in a heavy-duty freezer bag and pounded with a blunt, heavy object to a sand and pebble texture
2 large eggs
1 tablespoon Dijon mustard
1 teaspoon dried thyme
3/4 teaspoon salt
1/2 teaspoon ground black pepper
1/2 teaspoon dried oregano
1/4 teaspoon garlic powder
1/4 teaspoon cayenne (optional)
4 chicken leg quarters, separated into drumsticks and thighs, skin removed, and patted dry with paper towels
1. Adjust oven rack to upper-middle position and heat oven to 400 degrees. Line sheet pan with foil and set large flat wire rack over sheet pan.
2. Drizzle vegetable oil over Melba toast crumbs in a shallow dish or pie plate; toss well to coat. Mix eggs, mustard, thyme, salt, pepper, oregano, garlic powder, and optional cayenne with a fork in a second shallow dish or pie plate.
3. Working one piece at a time, coat chicken on both sides with egg mixture. Set chicken in Melba crumbs, sprinkle crumbs over chicken, and press to coat. Turn chicken over and repeat on other side. Gently shake off excess and place on rack. Bake until chicken is deep nutty brown and juices run clear, about 40 minutes.