Heat a dash of oil in a large, deep frying pan or wok. Add the red onion and garlic, and cook over a medium heat for at least 5 minutes, until soft and fragrant (you don't want it to brown).

Add the uncooked rice, and cook over the heat for 1-2 minutes, stirring constantly. Then add the vegetable stock a little at a time (I usually add about 250ml / 1 cup at a time), stirring regularly and allowing any excess liquid to be mostly absorbed each time before adding more. Continue cooking the rice like this until it's cooked to your liking - I needed around 5 cups of stock in total, but you don't need to use the full amount, or you can use a little more, depending on your preference.

Remove the flesh from the avocados, and cut into small chunks. Use a fork to mix it into the risotto, mashing some of the avocado and leaving some of the chunks whole. Add the lemon juice, chopped herbs, and salt and pepper to taste, and mix well to combine. Make sure the risotto is piping hot, then serve.