Heat the oil in a large pan over medium heat. Add the onion and cook for 5 minutes until soft.
Add the garlic, cumin, coriander and chilli powder. Cook for 1 minute until fragrant.
Add the chopped carrots, red lentils, chopped tomatoes and vegetable stock. Stir well.
Bring to the boil, then reduce heat and simmer for 20 minutes until the lentils are soft and the carrots are tender.
Remove from heat and blend with a stick blender or in a food processor until smooth.
Season with salt and pepper to taste. Add a splash of water if the soup is too thick.