Heat the olive oil in a large pan over medium heat. Add the onion and cook until translucent, about 5 minutes.
Add the Arborio rice and stir to coat the grains with the oil.
Begin adding the warm vegetable stock, one ladle at a time, stirring constantly until the liquid is absorbed before adding more.
Continue this process until the rice is creamy and cooked through, about 18-20 minutes.
Stir in the peas, Parmesan cheese, mint, lemon juice, and zest. Season with salt and pepper to taste.
Serve immediately, garnished with additional mint and Parmesan if desired.