Begin by heating the vegetable broth in a saucepan until it's just simmering, then reduce to low heat to keep warm throughout cooking.
In a large heavy-bottomed pan, warm the olive oil over medium heat. Add the finely chopped onion and cook, stirring often, until it becomes translucent and fragrant—about 3-4 minutes.
Add the Arborio rice to the pan and stir constantly, allowing the edges to turn translucent and the rice to toast lightly—about 2 minutes. This helps release the starch for creaminess.
Pour in the white wine and stir until it’s mostly absorbed, which should take about 2 minutes. You’ll notice the rice shimmering and smelling slightly alky.
Begin adding the warm broth, one ladleful (about 1/2 cup) at a time, stirring constantly. Wait until most of the liquid is absorbed before adding more, maintaining a gentle simmer.
When the rice has absorbed about half the broth, stir in the green peas. Continue adding broth and stirring, allowing the peas to soften and release their sweet aroma—about 3-4 minutes.
Keep adding broth and stirring until the rice is tender but still slightly al dente, with a creamy texture—about 20 minutes total. The risotto should be luscious and coat the back of a spoon.
Turn off the heat and gently fold in the grated Parmesan cheese, stirring until it melts into the risotto. Add the knob of butter and lemon zest for extra richness and brightness, stirring until well combined.
Let the risotto rest for 2 minutes off the heat to allow flavors to meld, then give it a final stir. The dish should be glossy, vibrant green from the peas, and ready to serve immediately.
