In a small bowl, stir together crushed nuts, salt, black pepper and rosemary (and parmesan if adding). Pour flour into a separate bowl or plate, can add a pinch of salt and pepper into that too. Pat dry the fillets with paper towels and roll in flour.
In another bowl, beat the egg. Dredge each piece of the fish with egg (or could brush with mayonnaise instead.) Then roll each filet in the nut mixture to coat the outside.
Lay inside a sprayed 9x9 dish. Preheat oven to 400 F. Bake for 12-13 minutes, or until flaky in the thickest part. Allow to rest for 5 minutes before serving.