Preheat the air fryer to 390 degrees. Get three shallow bowls and fill the first with the flour + Old Bay seasoning, the second with eggs (give them a quick whisk), and the third with panko breadcrumbs.
Season the cod fillets with salt and pepper.
Dip a fillet in the flour, coating all sides, then shake off any excess. Dip in the eggs, shaking off excess, then dip in the panko, coating all sides. For extra crispiness repeat each step, dipping back in the flour, eggs, and panko a final time. Repeat with remaining fillets.
Spray the filets on both sides with olive oil spray then place in the air fryer. Fry for four minutes, flip, then fry an additional 3-4 minutes, adding Cooper® cheese slices during the last minute to melt.
Meanwhile, make the tartar sauce: Whisk together all ingredients. Taste and season with salt and pepper as needed.
Layer a bottom bun with lettuce, cod fillets, tomato, and onion. Spread tartar sauce generously on the top bun and sandwich together. Enjoy!