Heat oil in a large saucepan over medium heat. Stir and cook the chilli paste, cumin and 1 tablespoon of coriander until fragrant, about 1 minute. Add the ginger, onion and garlic; cook until the onions are soft and translucent, about 5 minutes. Place the potatoes and carrots into the pan with the onion mixture and cook for an additional 5 minutes.
Pour the vegetable stock and coconut milk over the cooked vegetables. Turn the heat to medium-high and bring to the boil, stirring occasionally. Reduce the heat to medium-low and simmer for 30 to 45 minutes or until the potatoes and carrots are soft.
Remove the pan from the heat and stir in the lime juice. Working in batches, puree the soup in a liqudiser or food processor until smooth. Serve hot or chilled, garnished with the remaining coriander.