Peel and chop butternut squash. Place in an ovenproof dish, toss with a little olive oil and roast at 180 C / Gas 4 for 15 minutes.
Pierce sweet potatoes and place in microwave for 5 minutes or until soft.
Chop the onions, garlic and chilli. Add to a saucepan and cook on a medium heat in a little olive oil until soft. Place butternut squash and peeled sweet potatoes into pan and cover with vegetable stock. Simmer for 20 to 25 minutes.
Add grated ginger and natural yoghurt, then blend until it reaches desired consistency.