Heat the chicken stock to boiling in a saucepan, then reduce the heat and hold at a simmer.
Heat the butter and oil in a wide heavy saucepan over low heat. Add the onions and cook until translucent, about 5 minutes. Add the rice and cook, stirring to coat with butter, until opaque, about 3 minutes.
Add ½ cup hot stock and cook, stirring constantly, until the stock is absorbed. Continue adding the stock, ½ cup at a time, and stirring until the rice is about half cooked. Add the pancetta and all the vegetables except the zucchini; cook about 5 minutes more, adding stock as needed. Add the zucchini and herbs for the last minute or two. Stop cooking when the rice is al dente in the center and creamy on the outside. Season with salt and pepper to taste. Leave the risotto a little soupy. Sprinkle with the Parmesan and serve at once.