Heat a wide pan over medium heat and add olive oil. Once shimmering and fragrant, add the diced onion and cook, stirring occasionally, until translucent and soft, about 5 minutes, filling the kitchen with a gentle aroma.
Add the Arborio rice to the pan and stir to coat each grain with oil. Toast for about 2 minutes until the edges look slightly translucent and it smells nutty, making sure not to brown the rice.
Pour in the white wine and stir until it mostly evaporates, about 1-2 minutes. The rice should shimmer and smell subtly sweet as the alcohol cooks off.
Begin ladling in the warm vegetable broth, about 1 cup at a time. Stir constantly and wait until the liquid is nearly absorbed before adding the next ladle. Repeat this process, stirring gently, for about 18-20 minutes, until the rice is tender but still has a slight bite and the mixture is creamy.
In the last 5 minutes, add the frozen peas directly from the freezer, stirring to incorporate. Continue cooking until the peas are tender and the risotto is a vibrant green, with a glossy, luscious consistency.
Remove the pan from heat, then stir in the grated Parmesan, butter (if using), and lemon zest for a bright finish. Mix until the cheese and butter melt into the creamy rice, and the dish looks glossy and inviting.
Let the risotto rest, uncovered, for about 2 minutes. This helps the flavors meld and the texture settle into a perfect, slightly thickened consistency.
Spoon the vibrant green risotto into bowls, garnished with extra Parmesan or a drizzle of olive oil if desired. Serve immediately while hot, with the peas still bright and the grains tender yet al dente.
