In a large non-stick frying pan, cook the lamb, onion and carrots, stirring often, until the lamb is browned and veg is starting to soften, about 8 mins. Add the garam masala and some seasoning and cook for a further 2 mins until fragrant. Pour in the stock, bring to the boil, tip in the peas and cook for a further 2 mins until the peas are cooked and most of the liquid has evaporated.
Meanwhile, cook potatoes in a large pan of salted water until just tender, about 8 mins. Drain well, return to the pan and gently stir in turmeric and coriander – try not to break up the potatoes too much.
Heat oven to 200C/180C fan/gas 6. Transfer the mince to a baking dish and top with the turmeric potatoes. Squeeze over the lemon juice, then bake for 30-35 mins until potatoes are golden. Serve immediately with extra lemon wedges on the side.