Heat a generous tablespoon of olive oil in a large, heavy-bottomed pan over medium heat until shimmering and fragrant.
Add the finely chopped onion and sauté, stirring frequently, until translucent and soft, about 4-5 minutes. The onions should look slightly glossy and smell sweet.
Stir in the minced garlic and cook for another minute until fragrant, being careful not to burn it.
Add the chopped pumpkin to the pan and cook, stirring occasionally, until it begins to soften and turn tender, about 8-10 minutes. The pumpkin should become velvety and slightly caramelized around the edges.
Pour in a ladleful of warm vegetable broth and stir gently until the liquid is mostly absorbed, allowing the pumpkin to break down slightly.
Add the Arborio rice and stir constantly, letting each grain toast slightly and absorb the flavors, about 2 minutes. The rice should look glossy and translucent around the edges.
Gradually add the warm broth, one ladle at a time, stirring continuously and letting each addition absorb before adding the next. Continue this process for about 20 minutes, until the rice is creamy and al dente, with a slight bite in the center.
Once the rice reaches your desired consistency, stir in the butter, grated Parmesan, and lemon juice or zest. Taste and season with salt and pepper as needed.
Cook for another 2 minutes on low heat, allowing the flavors to meld and the risotto to become luxuriously creamy.
Serve hot, garnished with extra Parmesan and a squeeze of lemon if desired. Enjoy the comforting warmth of this seasonal pumpkin risotto.
