Peel the onion and finely chop. Peel the garlic clove and finely chop. Halve the chilli, flicking out the seeds and membrane for less heat, and finely chop. Slice the chestnut mushrooms. Trim the root off the cabbage, and finely shred the leaves.
Pour 1 tbsp oil into a pan and warm to a medium heat. Tip in the onion, garlic and chilli. Sprinkle in a little salt and pepper and cook for 2-3 mins.
Add the mushrooms and cook for 3-4 mins stirring frequently, till glossy.
Crumble the stock cube into the pan and spoon in 1 tbsp peanut butter. Pour over 750ml boiling water and stir well till the stock cube and peanut butter have dissolved. Bring to the boil, then reduce to a simmer. Cover the pan with a lid and cook for 10 mins.
Stir in the cabbage leaves. Continue to simmer for 5 mins, till just tender. Squeeze in the lime juice and taste the soup. Add a little salt and pepper if needed, then ladle into bowls and serve.