Spray a non-stick saucepan with Fry Light and cook the leeks for 5-6 minutes until soft and beginning to change colour. Stir in the squash, allspice and nutmeg and continue to cook for 1 minute. Pour in the stock, add the seasoning and bring to the boil. Stir in the coriander, cover and simmer for 35 minutes until the squash is soft. Transfer the soup into a blender and puree. Return the soup to the saucepan, stir in the milk and gently reheat, do not boil. Season to taste, Pour into serving bowls with a swirl of yogurt and sprinkled with the coriander.