Chop the onion and carrots. Peel and dice the potatoes. Slice the celery.
Heat the oil in a pan and fry the paste and garlic for a minute until fragrant, while constantly stirring.
Pour in the vegetable broth, stir, then add the rest of the ingredients.
Bring it to the boil and simmer, under cover, at a low temperature for about 30-40 minutes.
When the lentils have softened, remove from the heat and blend in a liquidizer or with a hand-held blender - the soup should be textured not too smooth!
Serve warm.