Place the lentils in a large bowl and rinse several times in cold water to clean them.
In a large pot, heat the olive oil over a medium heat and saute the onion for 2 minutes. Add the garlic and saute for 1 minute and then add the ginger, chilli, ground coriander and cumin, turmeric and saute for a further minute.
Add the carrot, celery, red pepper and tomato and stir. Place the washed lentils on top.
Pour in 1½ litres of cold water, add a pinch of salt. Cover and bring to a boil, lower the heat and simmer for 30 minutes.
When the soup is cooked stir well, season with salt and pepper and stir in the chopped fresh coriander.