Cut the fish fillets into pieces, fry in light olive oil with the lemon slices and coriander stalks for 2 minutes.
Mix together the prawns, avocado, tomato, onion, chilli, coriander leaves, orange and lime juice with the chilli ketchup. Toss with the fish.
Chill for about 10-15 minutes. Serve on a bed of mixed leaves or put in a sterilsed jam jar.