Wash and trim the spring onions and cut the white and light green parts into rings. Peel and slice the garlic. Peel and slice the bananas. Wash, halve and deseed the chilli and cut into thin strips.
Heat the groundnut oil in a pan and sweat the spring onions and garlic for about 1 minute. Add the vegetable stock and coconut milk and season with the soy sauce, sugar, salt and pepper.
Simmer the soup for about 5 minutes. Add half the banana slices and chilli and bring to the boil. Remove from the heat and puree. Add the rest of the banana slices and chilli and simmer for a further 3 minutes. Serve immediately.