Cut one lemon half into slices or wedges; set aside. Juice the remaining lemon half into a large bowl. For slaw, combine mayonnaise and honey with juice; reserve 2 tablespoons juice mixture. Stir celery, apple, and cabbage into juice mixture in bowl; set aside.
Sprinkle catfish fillets with salt and brush with reserved juice mixture. In a shallow dish combine cornmeal and chili powder; coat fish with mixture.