Heat the olive oil in a saucepan, add the onion and spring onion and fry for 4-5 minutes, or until softened but not browned. Add the garlic and fry for a further minute.
Add the chopped sweet potato, stock and soy sauce and simmer for 6-8 minutes, or until the sweet potato is tender.
Stir in the olives and rocket and then pour into a bowl. Garnish with dill and serve.
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Guests in this edition are natural history TV presenters Chris Packham and Nick Baker.