Melt the butter in a heavy bottomed pan. Add diced onions and peppers then gently fry until softened.
Stir in the rice and increase heat, stirring consistently for 1-2 mins.
Add the lemon juice plus one ladle of hot stock, and bring to a boil over a medium-high heat, stirring constantly until almost absorbed.
Add in the sliced courgette and stir for about a minute.
When the liquid has just about been absorbed, add another ladle of stock. Continue adding one ladle of stock at a time after the previous stock has been absorbed, This will take 20-25 minutes until the rice is just tender and creamy.
Stir in the Parmesan, mascarpone and some salt & pepper plus thyme, lower heat and cover.
Garnish with pine nuts and lemon zest before serving.