Prepare the vegetables. Finely chop the onion and crush the garlic. Cut the peeled potatoes into 75-100g pieces. Roughly chop the mint.

Heat a large pan, add the lamb and cook quickly to draw the fat from the meat. Add the chopped onion with the oregano, reduce the heat and cook for 5-6 minutes, until the onion is softened. Add the garlic with the tomatoes, half a tomato can of water and the tomato purée. Stir in the mint with some salt and pepper, then simmer for 20 minutes, or until reduced to a thick sauce. Zest the lemon into the lamb and stir.

Bring the potatoes to the boil in a pan of cold water then cover and simmer for 15 minutes while the lamb is cooking. Drain and allow to cool slightly, then cut into thick slices. Preheat the oven to gas mark 6, 200°C. Grate the Orkney Cheddar.

Season the lamb, then spoon half into the bottom of a large baking dish and top with half the potato. Scatter about a third of the cheese over then repeat the meat and potato layers.

Make the sauce. Melt the butter in a saucepan, add the flour and stir to blend then cook over a low heat for a minute or so. Gradually add half the milk, off the heat, stirring thoroughly after each addition, then add the remainder. Bring to the boil stirring all the time then season with salt and pepper and add most of the remaining cheese. Spread the sauce over the top layer of potato and scatter the remaining cheese over.

Set the dish on a baking tray to catch any drips then bake in the hot oven for 30-40 minutes, until the topping has browned. Serve with fresh green vegetables, or a tomato and onion salad.