Heat the oil in a large pot and add the cumin seeds, chilli flakes and ginger. Fry for a minute then add the onion, garlic and sugar stirring for a few minutes over medium-low heat until onion is soft.
Add the sweet potato, parsnip and tomatoes and stir for a couple of minutes.
Add the stock, bring to the boil and then simmer for about 15 minutes or until vegetables are tender.
Pulse the soup in a blender (or use an immersion blender) until smooth.
Return to the pot then stir in the peanut butter.
Check the seasoning and serve with a sprinkling of chilli flakes, a handful of chopped roasted peanuts, and a drizzle of oil.