Heat the chicken stock in a small heavy-bottomed saucepan until it simmers. Pull the saucepan to the outer periphery of the burner or if your range is electric lower the heat setting and keep the stock just below a simmer throughout cooking.
Melt the butter in a heavy-bottomed 3-quart saucepan over low heat until it foams. Add the shallots and prosciutto and sauté, stirring with a wooden spoon until the shallots are translucent and have nearly melted into the butter, about 5 minutes. Add the rice, increase the heat to medium, and sauté, stirring until the grains are coated with butter and have turned opaque, about 2 minutes.
Add the wine, stir, and reduce to a glaze over medium-low heat. Ladle in 1 cup of hot stock and add the thyme, bay leaf, ½ teaspoon salt, and ½ teaspoon pepper; stir once to make sure the grains are just covered with liquid. Cook the rice, uncovered, at the barest simmer, until the liquid has nearly evaporated and the rice begins to look dry. Add another ladle of hot stock. Continue to cook the risotto in this fashion, adding stock as needed, until the rice grains have expanded and no longer have a hard starch center, about 20 minutes. Stir in the Parmesan. The risotto should look creamy but not wet. Taste for seasoning. Stir in the peas and lemon zest and serve immediately.