Heat your oven to 180°C/Fan 160°C/Gas 4. Weigh out 300g of potatoes. Scrub and chop them. Pop them in a pan of boiling salted water. Cover and bring to the boil. Simmer for 15 mins till the potatoes are very soft.
While the potatoes cook, fill a deep frying pan with water and bring it to the boil. Pick the leaves off the parsley stalks and finely chop. Set aside. Add the parsley stalks to the pan of water with 1 tsp black peppercorns.
When the water is boiling, add the fish pie mix. Simmer for 8-10 mins till the fish is cooked. Drain, then discard the parsley stalks and peppercorns. Peel and grate the shallots. Finely grate the zest from the lemon. Slice the lemon into wedges.
Drain the potatoes and mash them in a bowl. Tip in the fish and mash with the potatoes. Mix in the shallots, lemon zest, half the parsley leaves and some seasoning. Divide into 6 portions and shape into fish cakes. Grease a baking tray with ½ tbsp oil.
Beat the egg in a bowl. Put the flour and breadcrumbs onto two plates. Dip the fish cakes in flour, then egg, then breadcrumbs. Put them on the baking tray. Bake in the middle of the oven for 30-35 mins till golden and cooked through.
Trim the courgettes and carrots and slice into batons. Tip them into a bowl. Add 1 tbsp oil and some seasoning. Toss to mix.
Spread the courgette and carrot chips out on a large baking tray or roasting tin. Roast them at the top of the oven for 25-30 mins till they’re soft and a little charred.
Serve the fishcakes with the courgette and carrot chips and lemon wedges for squeezing.