Heat oil in casserole and cook cumin seeds and onion over medium heat for 5-6 mins until onion is caramelised. Add garlic, ginger, potato, cauliflower, turmeric and chilli and turn until evenly coated with the spices. Add the tomatoes, salt and 300ml water.
Bring to the boil, reduce heat, cover and simmer for 15 mins or until tender. Stir in garam masala and simmer for further 2 mins. Garnish with fresh coriander.