Heat oil in a large saucepan or pot. Add leek and garlic, cooking for 5 minutes until leek is tender. Add stock, sweet potato, superblend mix and green beans. Bring to the boil, reduce heat and simmer for 10 minutes.
Stir in tomatoes and balsamic. Season well. Cook a further 5 minutes. Serve soup with some freshly torn basil leaves stirred through.