Preheat the oven to 180C/350F
Drizzle 1 tbsp of the sunflower oil into a baking tray, add a good pinch of cumin seeds and the cauliflower florets and roast in the oven for 10 - 15 minutes until just beginning to brown.
Heat the rest of the sunflower oil in a large, heavy bottomed, frying pan.
Add the chopped leeks, cover and fry for 5 minutes until soft.
Add the ginger and garlic and fry gently for a further minute.
Add the rest of the cumin seeds, the coriander, paprika, curry powder, turmeric and the cinnamon stick and fry for a few seconds until aromatic.
Add the potatoes and stir to cover with the spice mix.
Crumble in the stock cube, add the coconut milk and water and cook for 15-20 minutes until the potatoes are soft.
Add the tomatoes, the beans and the roasted cauliflower, stir and cook, covered for a further 5 minutes until the beans are cooked. Add more water if the sauce is too dry.
Serve, topped with chopped red chilli and warm naan bread on the side.