Heat the olive oil in a large pot over medium heat. Add the onion, garlic, carrots and sweet potato and sauté for 5-7 minutes until softened.
Stir in the cumin, cinnamon, ginger and turmeric and cook for another minute.
Add the lentils, vegetable stock and chopped tomatoes and bring to a boil, then reduce heat and allow to simmer for 30-35 minutes.
When the lentils and sweet potato are tender, stir in the lemon juice and season to taste.
Serve piping hot, with fresh coriander and a swirl of yoghurt.
Stir in the lemon juice and adjust seasoning if needed. Garnish with fresh coriander before serving.
