Cut the tops off the peppers, and carefully remove the core and seeds. Reserve the tops and hulls of the peppers.
Wash the tomatoes and remove the stalks. Plunge them into boiling water for a few minutes until the skin starts to detach. Remove the skins then loosely crush them in a bowl. Wash and chop the chilli finely, and peel and finely chop the garlic. Thin out the leaves from the bunch of basil and loosely chop.
Heat half the oil in a large casserole dish, then add the peppers (placing them vertically, open top upwards), lower the heat and cook for 10 minutes.
Cook the cod in boiling water for 5 minutes then drain it and thin out the slices. 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 and mix well.
Preheat the oven to 180°C / Gas Mark 6.
Take the peppers and gently stuff them with the cod, tomato and garlic mixture and place them in an ovenproof dish. Place 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, remove the foil, and sprinkle with the grates parmesan and serve.