Preheat oven to 400 degrees. Fit a baking sheet with a wire rack and coat with cooking spray. Set aside.
Place pistachios, breadcrumbs, ¼ teaspoon salt and a pinch of black pepper in the bowl of a food processor. Pulse until large crumbs form.
Place in a shallow bowl and set aside. In another shallow bowl, whisk together eggs and Dijon mustard until combined.
Season cod filets with remaining salt and pepper. Dip each filet into the egg mixture, then generously coat it with pistachio mixture. Line on the baking sheet, coat with cooking spray and bake 10-12 minutes, until just flaky.