Gently fry the onion over a low hear with a dash of extra-virgin olive oil. Add the pumpkin and sauté until soft.
Add the rice, stir and then add salt and pepper and pour in the walnut drink. Cover and cook for a few minutes over a low heat, until the liquid starts to be soaked up by the rice.
Add the vegetable stock and keep cooking over a low heat, stirring all the while, for about 25 to 30 minutes.
Just before the end, add the Parmesan cheese and stir. Serve with a decorative basil leaf.