Preheat the air fryer: Set your air fryer to 390°F (200°C). Preheating helps the crust crisp up right away.
Prep the cod: Pat the fillets dry with paper towels.
Removing surface moisture is key to a crisp crust and even browning.
Mix the wet coating: In a small bowl, whisk together olive oil, Dijon mustard, lemon juice, lemon zest, and garlic. This tangy mixture helps the crumbs stick and adds flavor.
Make the herb crumb: In another bowl, combine panko, parsley, dill, thyme, salt, pepper, and red pepper flakes if using. Stir to distribute the herbs evenly.
Coat the fillets: Brush the top of each fillet with the Dijon-lemon mixture.
Press the herb crumb mixture onto the coated side, packing gently so it adheres. Leave the underside bare so it cooks evenly.
Prepare the basket: Lightly spray the air fryer basket with oil to prevent sticking. You can also use a perforated parchment liner safe for air fryers.
Arrange the fish: Place cod in the basket crumb-side up in a single layer, leaving space between fillets for airflow.
Air fry: Cook for 8–10 minutes, depending on thickness.
The cod is done when it flakes easily with a fork and reaches an internal temperature of 145°F (63°C).
Finish and serve: Let the fillets rest for 1 minute. Squeeze fresh lemon over the top and serve with your favorite sides.