Preheat the oven to 180°C / 350°F / Gas mark 4.
Cut the tops off the peppers, and carefully remove the core and seeds.
Reserve the tops and hulls of the peppers.
Plunge the tomatoes whole, into boiling water for a few minutes until the skin starts to detach.
Heat half the oil in a large casserole dish, then add the peppers (placing them open top upwards), lower the heat and cook for 10 minutes.
Bring a kettle to boil and cook the cod in boiling water for 5 minutes then drain it and flake into a bowl.
Heat the remaining oil in a pan and then add the cod, tomatoes and garlic, cook for 5 minutes then turn the heat off and add the basil and chilli pepper if using and mix well.
Stuff the peppers with the cod, tomato and garlic mixture and place them in the ovenproof dish.
Pop the lids back onto the peppers, cover them loosely with foil and then place into the oven.
Cook for 15 minutes.
Remove from the oven, and sprinkle with the parmesan and serve.