Place the water and milk in a saucepan and bring to the boil. Add the rosemary. Place the cod steaks in the saucepan and bring the liquid back to the boil. Once at boiling point, cover the pan and remove from the heat. Set aside for 10 minutes, keeping the lid or cover closed.
Wash the courgettes and cut off both ends. Take 3 courgettes and use a mandolin to cut them into fine strips. If you do not have a mandolin, carefully slice the courgettes into strips about 3 mm thick. Lay these strips on a baking tray or other flat surface and sprinkle with salt - this will absorb the moisture. Take the other 3 courgettes and dice them into small cubes.
Heat a non-stick frying pan, add a drizzle of olive oil and fry the cubes of courgettes over a medium heat. Season and remove from the heat once they start to colour.
Preheat your grill.
Strain the cod (keeping the liquid aside) and remove the skin and bones. Cut the cod into small cubes and then place in a bowl with a spoonful of the cooking juices. Add the cubed courgette and mix well.
Take a long strip of courgette and place a spoonful of the cod and courgette mixture at one end of the strip. Roll the strip up so that it resembles a canneloni and then place in an oven-proof dish. Repeat this process until you have used all of the cod and courgette. Sprinkle the parmesan over the dish and place under the preheated grill. Grill until the cheese has melted and turned a golden brown.
Serve with some fresh, crisp salad leaves.
«This dish can be made with other types of firm, white fish.»