Heat the olive oil in a large pan. Add the onion and cook for 5 minutes until soft.
Add the garlic, courgette and red pepper. Cook for 3 minutes.
Add the rice and stir for 1 minute until the grains are coated and slightly translucent.
Add a ladleful of warm stock and stir until absorbed. Continue adding stock one ladle at a time, stirring frequently, for about 18 minutes.
When the rice is nearly done and the stock is used up, add the frozen peas and cook for 2 more minutes.
Remove from heat. Stir in the butter and most of the parmesan. Season well. Serve topped with the remaining parmesan.