In a small saucepan, bring the vegetable stock to a boil, then keep warm over low heat.
In a large skillet, warm the olive oil over medium-low heat. Add the onions and garlic and cook, stirring occasionally, until the onions are translucent, about 5 minutes. Add the rice and continue cooking, stirring occasionally, until it's lightly toasted and opaque, about 2 minutes.
Add the wine and cook over medium-low heat until absorbed, about 5 minutes. Ladle 1 cup of the stock over the rice and simmer, stirring frequently, until absorbed. Continue to add the stock ½ cup at a time, stirring frequently, until the rice is creamy and tender but still slightly chewy in the center, about 20 minutes.
Meanwhile, in a medium skillet, cook the chorizo over medium-high heat until lightly browned, about 5 minutes. Stir the chorizo, the ¼ cup of scallions and the chiles into the risotto until combined. Add the Parmesan and season to taste with salt and pepper.
Divide the risotto among 4 plates and garnish with additional scallions and Parmesan if desired. Serve immediately.