Heat the oil in the saucepan, add the onion and sweat until translucent. Add the ginger and garlic and sauté for 1 - 2 minutes.
Add the diced sweet potato, the water and the salt and bring to the boil. Reduce the heat and simmer for 15-20 minutes until the sweet potatoes are tender.
Add the tomatoes, the peanuts or peanut butter, allspice and chili sauce. Puree with the magic wand and heat again. Garnish with coriander leaves or spring onions.