Heat the oil and cook the onion for 5 minutes in a covered saucepan, without colouring. Add the dried spices and cook, stirring, for 5 minutes.
Add the lentils and stock. Cover and bring to the boil. Simmer gently for about 20 minutes until the lentils are tender. Add the tomatoes and simmer for 10 minutes.
Cool a little then puree in a liquidiser withthe fresh coriander leaves. Check seasoning.
Heat the oil for the garnish and saute the chopped fresh green chilli for 2 minutes over a moderate heat.
Serve the soup garnished with the sauted chilli and fresh coriander leaves.