In a large saucepan, heat the sunflower oil
Add the onion and cumin seeds and saute until the onion is soft, stirring frequently
Add the lentils and the stock
Add the garam masala and mixed herbs
Stir well and bring back to the boil
Simmer for 20 minutes until the lentils are soft
Add the chopped tomatoes and tomato puree
Stir and bring back to the boil
Add the lemon juice
Season with salt and black pepper
Liquidise and return to the pan
Adjust seasoning reheat and serve