Add buttermilk to a bowl and gently place the catfish fillets (or nuggets) into the milk. If you don't have buttermilk, it is easy to make by adding lemon juice to milk. Soak the fish for 30 minutes. This step is important to remove the fishy flavor from the catfish.
Mix up the cornmeal seasoning mix in a large bag. Place the cornmeal fish breading and seasoning ingredients into a large bag and shake to mix it up. When the catfish is done soaking in buttermilk, hold the catfish over the bowl to allow the extra milk to run off.
Place the catfish in the bag, one fillet at a time. Shake gently so the raw catfish fillet is coated in the catfish breading mixture. Preheat your air fryer to 375º F.
Spray the bottom grill of the air fryer with a high heat oil like avocado or canola. (Do not use olive oil or another heat intolerant oil or your fish will turn out rancid.) Place a breaded catfish fillet in the air fryer. Make sure the fish isn't touching so the air can circulate around each piece of fish.
Spray the top of the gluten free breaded catfish with more oil. This will help the crust get nice and crispy!
Cook your catfish in the air fryer for 12-15 minutes. The actual cook time will vary depending on the size of your catfish fillets, and whether you use catfish nuggets or fillets. You will know the catfish is done cooking when it is crispy and the cornmeal breading is a golden color.
Note, many will recommend flipping your catfish over partway through the cooking cycle. I find this difficult without the catfish falling apart in the air fryer. It is up to you if you want to try this. I did not flip it and my catfish was still crispy and delicious on both sides.
Drizzle fresh lemon juice over the fish and enjoy!