Heat a skillet and add 2 tablespoons of olive oil. Sauté the onion over moderate heat for 5–6 minutes until the onion is translucent. Add the garlic and sauté for another minute.
Add the crushed red pepper and sliced fennel and sauté for another 3–4 minutes. Add the chopped peppers and tomatoes and cook for another 3 minutes Add the wine and cook for a few minutes until mostly evaporated, and then add the stock. Cover and cook for about 5-6 minutes. Add the olives, and cook until the fennel is very tender.
Meanwhile, bring a large pot of water to a rolling boil, add a tablespoon of salt, and cook the pasta for 9-11 minutes depending on package directions. Reserve 1 cup of hot pasta water before you drain the pasta in a colander.
While the pasta is cooking, add the chopped sausage pieces to the fennel mixture. Cook uncovered for about 5-6 more minutes. Taste carefully, and add a little sea salt and freshly ground black pepper.
Serve immediately with the optional grated Parmigiano-Reggiano.