Heat the oil in a large pan then add the onions, ginger and garlic and fry for 5 minutes until starting to soften. Stir in the chilli and spices and cook for 2 minutes more. Add the stock, vegetables and lentils, cover and simmer for 30 minutes until the vegetables are tender.
Blitz with a hand blender or in a food processor until smooth. Stir in the milk, coriander and the greek yogurt if using.
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Freezing and defrosting guidelines
Make the soup, then leave to cool at room temperature. Freeze (without garnishes or toppings) in a rigid container, leaving a bit of space for expansion, for up to 1-3 months. Reheat either from frozen or defrost in the fridge overnight. Once piping hot, add toppings or garnishes and serve.