Preheat the broiler to high and lightly oil a large shallow heatproof dish. Arrange the fillets in the dish, slightly spaced apart, season with salt and pepper and brush them with a little oil. Broil for 2 minutes.
Remove the dish from the broiler, turn the fish over and top each fillet with a scrunched slice of ham. Mix together the cheese and scallions, scatter over the fish.
Return to the broiler for 5 minutes until the fish flakes easily when prodded with a knife.
Serve with green vegetables - broccoli or stir-fried cabbage would be good.