In a medium saucepan, bring the stock to a gentle simmer over low heat and keep it warm.
Heat the olive oil in a large, high-sided skillet or wide saucepan over medium heat. Add the onion and cook, stirring frequently, until softened and translucent, 5-7 minutes.
Add the rice to the skillet. Cook, stirring, until the grains are well coated and lightly toasted, 2-3 minutes.
Pour in the wine and cook, stirring, until most of the liquid has evaporated.
Add about 1/2 to 3/4 cup of the warm stock. Cook, stirring frequently, until the liquid is mostly absorbed.
Continue adding the stock a ladleful (about 1/2 cup) at a time, stirring often and letting each addition absorb before adding more, until the rice is creamy and just tender with a slight bite, 18-22 minutes. You may not need all the stock, or you may need to add a splash of hot water if the rice is still firm.
Stir in the butter until it melts. Then add the peas and cook, stirring, until they are bright and heated through, 3-4 minutes.
Stir in the lemon juice and the zest. Season to taste with salt and pepper.
Remove the pan from the heat and stir in the Parmesan until melted and creamy. Serve immediately, with extra Parmesan on the side if you like.