Heat the oil in a large saucepan, add the onion and leek and sauté for 4–5 minutes. Stir in the garlic, ginger and spices and cook for 1–2 minutes, then stir in the cabbage, broccoli and parsnip and cook for a further 1 minute. Add the stock, bring to the boil and simmer for 12–15 minutes, until the parsnip is soft.
Transfer the soup in batches to a food processor or blender and process until smooth, transferring each successive batch to a clean saucepan.
Juice the lemon with the spinach. Stir the juice into the soup and season to taste. Heat through gently, if necessary.
Ladle the soup into bowls and top with a dollop of natural yogurt and sprinkling of chopped coriander.