Heat the oil in a pan over high heat. When the oil is hot, add the fresh tuna fillet and cook until the tuna is lightly browned (1-2 minutes per side). Remove the tuna from the pan, allowing any excess oil to drain off and adjust the salt.
Heat the tomato sauce in another pan over low heat, and as soon as the sauce is hot add the tuna prepared as above and cut into cubes along with the chopped parsley. Cook for about 10 minutes and adjust the salt and pepper.
In the meantime, cook the pasta in a large pot of lightly salted boiling water for the time indicated on the package. Drain the pasta, dress with the prepared sauce and serve hot. Farfalle can be substituted for the fiocchi rigati.