Combine mayonnaise and Cajun seasoning in a small bowl. Place bread crumbs on a plate.
Spread Cajun mayonnaise on both sides of fish fillets with a small spatula or butter knife. Coat each fillet, one at a time, with bread crumbs. Lightly spray both sides of breaded fillets with cooking spray and transfer 2 fillets to each air fryer tray; do not overcrowd.
Turn an air fryer to the Roast setting (375 degrees F (190 degrees C) according to manufacturer's instructions and set timer to 14 minutes. Rotate trays at 7 minutes. Fish should flake easily with a fork.
Carefully remove fillets from the trays and serve.