Set the oven to 180°C/350°F/Gas Mark 4. Heat a solid-based pan and add the cumin and coriander seeds and cook for about 20-30 secs, stirring, until you can smell the seeds. Pour in the canned tomatoes and 300ml water and bring to the boil. Add the leeks, courgettes, carrots and chickpeas to the pan. Stir in the turmeric and seasoning.