Heat the oil in a saucepan over a medium heat. Add the garlic and onion and fry for 3-4 minutes, until golden and softened.
Add the chilli flakes and ground ginger and fry for one minute, then add the sweet potato and cook for 2-3 minutes.
Add the stock and coconut milk. Bring to the boil then reduce the heat to simmer for 8-10 minutes, then add the coriander.
Remove from the heat and allow to cool slightly, then pour into a food processor and blend until smooth. Season, to taste, with salt and freshly ground black pepper.
To serve, pour the soup into a warm bowl and garnish with the spinach leaves.
