Prepare lentils according to on-pack preparation instructions and set aside.
Heat the oil in a large pot and add onion and garlic, cooking until onion is tender. Stir in spices and cook for a further minute. Add pumpkin and tomato paste to pot, stirring well. Add stock, tomatoes, water, lentils and capsicum. Bring to the boil, reduce heat and simmer for 20 minutes until pumpkin and lentils are tender.
Stir in coriander. Season to taste and serve soup with yoghurt and extra coriander.