Heat a large nonstick skillet over medium-high heat. Sprinkle fish evenly with Cajun seasoning and salt. Coat pan with cooking spray. Add 2 fillets to pan; cook 4 minutes on each side or until fish flakes easily when tested with a fork. Remove fish from pan; keep warm. Wipe pan clean with paper towels; recoat with cooking spray. Repeat procedure with remaining 2 fillets.
While fish cooks, combine mayonnaise and remaining ingredients. Serve mayonnaise mixture with fish.