Bring a large pot of salted water to a boil over high heat. Heat 3 Tbs. of the olive oil in a 12-inch skillet over moderate heat. Add the garlic, chile flakes, and 2 Tbs. of the parsley and sauté briefly to release the fragrance of the seasonings. Add the tomatoes and fennel seed. Bring to a simmer, adjust the heat to maintain the simmer, and cook, stirring occasionally, until the sauce is thick and well blended, about 10 min.
Stir in the minced tuna and then the olives. Season with salt and remove from the heat while you cook the pasta.
Cook the pasta in rapidly boiling water. When the pasta is a few minutes away from being finished, return the tomato sauce to moderate heat and add enough of the hot pasta water -- about 2/3 cup -- to thin the sauce to a nice consistency. Keep the sauce warm over low heat.
When the pasta is about 1 min. shy of al dente, scoop out and set aside 1/2 cup of the pasta cooking water and then drain the pasta. Return the pasta to the hot pot and stir in the sauce. Cook together over moderately low heat for about 1 min., stirring and adding some of the reserved pasta water if needed to thin the sauce. Take the skillet off the heat and stir in the remaining 1 Tbs. olive oil. Serve the pasta immediately in warm bowls, garnishing each portion with a little of the remaining parsley.