Heat the oil in a large heavy-based frying pan and cook the onion and squash over a low to moderate heat for 10 minutes until softened. Add the rice and cook for 1 minute, then add half the stock. Bring to the boil, then reduce the heat and simmer gently for 5 minutes until almost all the stock has been absorbed, stirring occasionally.
Continue to add the stock 150 ml (¼ pint) at a time and cook over a gentle heat until the almost all the stock has been absorbed before adding more. Once the rice is tender, remove the pan from the heat, add the Parmesan, pine nuts and spinach and stir well to combine and wilt the spinach, returning to the heat for 1 minute if necessary.
Serve in warmed serving bowls with extra freshly grated Parmesan.