Heat the oil in a saucepan, add the onion and garlic and cook over a medium heat, stirring frequently, for 5 minutes. Add the carrots, potato and curry paste, stir well and then add the remaining ingredients. Bring to the boil, then reduce the heat, cover and simmer gently for 25 minutes.
Transfer to a food processor or blender and process until really smooth. Return to the pan and heat through.
Meanwhile, make the lime oil. Whisk the ingredients together in a bowl until combined.
Spoon the soup into serving bowls, drizzle over the lime oil and serve with crusty bread rolls.