Heat the vegetable oil in a large saucepan and gently fry the onion and garlic for 2 to 3 minutes, until softened. Add the carrots, swede or turnip and apple, and cook for another 2 minutes.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.Add the cooked chicken and peas and simmer gently for another 3 to 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.