Heat the oil in a saucepan, add the onion and garlic and fry gently for 5 minutes. Add the mushrooms and fry for 2 more minutes.
Stir in the chilli powder, kidney beans, carrot juice, tomato purée and a little salt and pepper. Bring to the boil, then turn down the heat, cover and simmer gently for 5 minutes.
Meanwhile, boil the sliced potatoes for 5 minutes then drain.
Transfer the bean mix to a 1.8 litre or similar ovenproof dish. Layer the potatoes over the top and scatter the cheese on top of that. Bake for about 30 minutes until the top is golden, then eat with a mixed leaf salad or broccoli.