Heat the olive oil into the casserole on medium heat, add the finely chopped onion and sweat it, stirring ocasionally with a woode spoon until it becomes transparent. Add the rice and continue stirring for 2-3 minutes. Then add the wine and leave it on medium heath for another 2-3 minutes, until all the alcohol evaporates completely.
Gradually add the vegetable stock, half a ladle at a time, stirring continually with a wooden spoon until the rice incorporates all the liquid. Add as much stock as it is necessary, and taste the rice from time to time, taking care that the rice remains "al dente". Continue to cook for about 15 minutes.
In the meantime, cut the courgettes into small cubes, add the lemon juice, some salt and pepper and gently fry them into olive oil, in a non-stick pan, for about 5-7 minutes.
When the risotto is done, take it off the heat, add the butter and the grated Parmigiano and continue stirring until it becomes creamy.
Add the courgettes and mix toghether with the risotto, then cover the casserole with a lid and leave it to rest for about 2 minutes.
Serve hot, with some freshly ground black pepper and some more grated Parmigiano Reggiano.