Heat the oil in a large pan, then add the onion and fry for 7 minutes or until softened. Add the garlic, chipotle paste and paprika and cook for 1 minute.
Stir in the sweet potatoes, carrots, stock, water and canned tomatoes. Bring to the boil, then reduce the heat and simmer, uncovered, for 25 minutes.
Stir in the spinach and lemon juice and cook for a further 2 minutes or until wilted.
Serve the sweet potato soup topped with a drizzle of yogurt, sprinkle of coriander and a wedge of lemon.