Heat the oil in a large pan and cook the onions until soft and starting to brown, about 8-10 mins. Push to one side of the pan and add the lamb. Leave the meat alone until the underside is browning, then break it down with the back of a spoon. Leave to brown for a few mins more, then stir in the ginger, garlic, spices and tomato purée. Stir for a few mins until the mixture is sticky and aromatic. Add 600ml water, the stock cube and the sugar.

Bring to a simmer, then lower the heat and cook for 45 mins, stirring occasionally to prevent it from sticking. The sauce should be thick but if it reduces too quickly, add a splash of water or cover with a lid.

Put the sweet potatoes and potatoes in a pan and cover with cold water. Bring to the boil, cover with a lid and simmer for 15 mins until tender. Drain and leave to steam dry for 10 mins.

Mash the potatoes with the cheese and some seasoning. Tip the mince into a baking dish about 20 x 35cm and 10cm deep. Stir in the peas. Cover with the mash, making dips and peaks with the back of your spoon, or pipe the mash on for a neater finish. Crush the poppadums in your hands and scatter over the mash, then drizzle over a little oil. You can now chill for up to two days or freeze for two months. If cooking straightaway, heat oven to 180C/160C fan/gas 4.

Bake for 45 mins until golden and bubbling around the edges. Leave to cool for 5 mins, then serve with the green chilli scattered over, if you like.