Preheat oven to 500°F. Spray a broiler pan or baking sheet with nonstick spray.
Place the flour in one shallow bowl and the buttermilk in another.
1 cup flour, 1 cup buttermilk
In a third shallow bowl, combine the panko breadcrumbs, parmesan cheese, salt, garlic powder, and pepper. Stir to mix.
1 cup seasoned Panko breadcrumbs, ¼ cup grated parmesan, 1 teaspoon salt, ½ teaspoon garlic powder, ½ teaspoon black pepper
Pat the cod fillets dry with paper towels.
1 pound cod, cut into 4 equal filets
Working with one fillet at a time, dredge it in the flour, shaking off any excess.
Dip the fillet in the buttermilk, then coat with the panko mixture, pressing gently so the crumbs stick on all sides.
Place coated fillets on the prepared baking sheet. Repeat with the remaining fish.
Bake for 15–17 minutes, or until the fish flakes easily with a fork and reaches an internal temperature of 145°F.
Serve hot with lemon wedges and tartar sauce, if desired.