How to Make It
In a large saucepan, combine the broth and Parmigiano-Reggiano rinds and bring to a boil. Simmer over moderately low heat until the rinds are very soft and the broth is reduced to 4 cups, about 30 minutes.
Meanwhile, in a large enameled cast-iron casserole, heat 2 tablespoons of the oil. Add the mushrooms and cook over high heat, stirring occasionally, until lightly browned, about 8 minutes. Add 3 tablespoons of the oil along with the zucchini, peppers and leek and season lightly with salt and pepper. Cook, stirring occasionally, until the vegetables are very lightly browned, about 5 minutes. Add the tomatoes and cook, stirring, until slightly broken down, about 2 minutes. Add the broth and the Parmigiano rinds and bring to a boil. Simmer over low heat until the vegetables are tender, about 20 minutes.
In a medium skillet, heat the remaining 1 tablespoon of olive oil. Add the broken pasta and cook over high heat, stirring constantly, until lightly browned, about 2 minutes. Stir the pasta into the stew and cook until al dente, about 2 minutes. Discard the rinds and stir in the basil. Serve the vegetable stew in deep bowls, passing toasted bread at the table.