Set up your breading stations with three shallow bowls. One with flour, one with beaten eggs and water, and the final one with panko breadcrumbs, salt, garlic powder, Cajun seasoning, and black pepper.
Dredge the cod filets through the flour, then into the beaten egg, and then through the breadcrumb mixture, coating well in each bowl.
Meanwhile, in a large heavy pot like a Dutch oven, heat the oil to 350 degrees. Using tongs, carefully add the fried fish to the hot oil. Fry for 4-5 minutes, flipping halfway through. Cook in small batches, so you don't overcrowd the pot.
Remove the fried fish to a paper towel-lined plate. Place the plate in the oven on warm while you cook the rest of the cod.
Notes
Store leftovers in an airtight container in the refrigerator for up to 3 days.
Reheat in the air-fryer at 350 degrees for 3-5 minutes or in the oven at 375 degrees for 7-10 minutes.