Stir in the curry powder and cumin seeds (if using) and cook gently for a few seconds. Pour in the reduced-salt stock and add the tomatoes. Bring up to the boil, then reduce the heat and simmer, partially covered, for about 20 minutes, or until the vegetables are tender.
For a Mediterranean flavour, use 1 tbsp of mixed dried Italian herbs instead of the cumin seeds and curry powder, and use basil instead of mint.
Add the cooked chicken and peas and simmer gently for another 3-4 minutes. Ladle the soup into warm bowls and serve each portion topped with 1 tablespoon of yoghurt and a few mint leaves (if using). Serve each portion with a wholemeal roll.
For a vegetarian version, omit the chicken and replace with a 400g can of chickpeas in water, drained, and make sure you use vegetable stock.