Start by making the salsa. Cut the papaya in half and remove the seeds. Remove the skin, cut the flesh into small dice and place into a bowl. Add the onion, chili, coriander, lime rind and juice, with salt to taste mix well and set aside.
Preheat a heavy-based frying pan over medium heat for about 10 minutes. Spread the Cajun spice on a plate. Brush the fish fillets with melted butter and dip them in the spices until well coated.
Place the fish in the hot pan and cook for 1 to 2 minutes on each side until blackened. Serve at once with the Papaya salsa. Garnish with lime and coriander.