Preheat the oven to 350 degrees F.: The kitchen should fill with a neutral warmth that signals even baking, which is essential because a steady oven temperature helps the arborio rice absorb liquid uniformly. You will not notice dramatic aromas at this point, but the consistent heat prevents hot spots that might cause uneven cooking. A common mistake is skipping preheating, which can lengthen bake time and produce unevenly cooked rice.
Add the olive oil to an oven-safe pan set over medium-low heat on the stovetop. Add the onion and stir to coat with olive oil. Cook for 2 minutes, stirring often.: As the oil warms you will see a gentle shimmer and a faint fruity scent if using a good quality olive oil , which helps the grated onion soften without browning. The moderate temperature gives you control and keeps the onion sweet rather than caramelized. Avoid turning the heat too high, because that will brown the ingredients prematurely and change the flavor balance.
Add the rice and stir to coat all of the grains.: The grated onion will hiss softly as it hits the warm oil, then settle and become translucent in a minute or two, releasing a mild sweet aroma. Stirring ensures even distribution so no pieces stick and crisp up. The pitfall here is rushing the step and not softening the onion enough, which leaves a sharp, raw bite.
Add the quart of broth, raise heat to high, and bring to a boil.: During this brief cook you will notice the texture changing from raw to tender and the smell shifting to gentle sweetness. Frequent stirring keeps the onion from catching and prevents uneven cooking, which would create browned pockets. A mistake to avoid is leaving the pan unattended, which can lead to uneven color and flavor.
Transfer pan to oven, cover with an oven-safe lid or foil, and bake for 20 minutes.: When you add the arborio rice it will look glossy as it absorbs the oil, and each grain should be thoroughly coated to promote even heat transfer and initial toasting. This step helps the rice maintain structure while it later releases starch for creaminess. Do not skip coating, because uncoated grains can cook unevenly and create textural inconsistency.
Remove from the oven, remove the lid, and stir in the zucchini, peas, additional broth, Parmesan, and butter, until combined and creamy. Serve warm topped with additional Parmesan cheese, lemon, and fresh herbs as desired.: Pouring in the warm to room temperature reduced sodium chicken broth will create an audible simmer that builds into a steady boil, releasing savory steam that deepens the dish's aroma. Bringing it to a boil activates the liquid absorption process quickly and evenly. If you start with a cold broth and barely warm the pan, the dish will take longer and may cook unevenly, so raise the heat until you see a rolling boil.
Transfer pan to oven, cover with an oven-safe lid or foil, and bake for 20 minutes: In the oven you will notice gentle bubbling beneath the lid, and the scent will become richer as the arborio rice hydrates and swells. The covered environment traps steam, which is the efficient mechanism that finishes the rice without constant stirring. A common error is using a pan that is not oven safe, or leaving the lid off, which causes excessive evaporation and may leave the rice undercooked.
Remove from the oven, remove the lid, and stir in the zucchini, peas, additional broth, Parmesan, and butter, until combined and creamy: When you take off the lid warm, fragrant steam will rise, and the rice should appear plump with some remaining surface broth. Stirring at this stage releases starch and creates a glossy, cohesive texture as Parmesan cheese melts and butter emulsifies. The diced zucchini and frozen petite peas will warm through in the hot rice without turning soggy. If your risotto seems too firm, add the additional half cup of reduced sodium chicken broth or water gradually, because adding too much at once can make the texture runny. Avoid over stirring aggressively, which can break grains and become gluey. Serve warm, and adjust seasoning with salt , pepper , or a squeeze of fresh lemon juice to brighten the finish.