Bring a large pot of water to a boil, add the spaghetti, and cook it until it is al dente, about 8 minutes.

While the spaghetti is cooking, mash the tuna with a fork.

When the spaghetti is done, spoon off a few tablespoons of the cooking water and reserve them, then drain the spaghetti.

Transfer the spaghetti to a large bowl and toss it with the tuna, using the reserved water to moisten the mixture if necessary.

If desired, add the Parmesan cheese and serve.

To make spaghetti alla corsara, add the tomato, garlic, and parsley to the spaghetti with the tuna, toss the ingredients well, and serve hot or at room temperature.