Heat olive oil in a Dutch oven or oven-safe deep saute pan over medium heat. Add the onions and cook, stirring occasionally, until softened, about 3-5 minutes. Add the rice and garlic and cook, stirring, until fragrant, about 1-2 minutes. Add the wine and simmer until mostly evaporated. Add the chicken broth and bring to a boil. Cover the pot and transfer to the oven. Bake until the rice is just tender, 50 minutes to 1 hour.
Shortly before the rice is done, steam asparagus, peas, and bell pepper until crisp-tender, about 4 minutes.
Fold the steamed vegetables, Parmesan, parsley, green onions, lemon zest, and pepper into the risotto. Serve immediately.