Fill a large pot with water, cover it, and bring it to a boil over high heat.

While the water heats, set a colander in the sink. Drain and rinse the cannellini beans in the colander.

Drain the tuna and break it into large flakes with your fingers or a fork. Set it aside on a plate.

Zest the lemon into a small bowl. Juice half of the lemon, and cut the remaining half into wedges for serving.

Chop the parsley and grate the Parmesan. Keep the Parmesan in two small piles so it is easy to divide later.

When the water reaches a full boil, add 2 teaspoons kosher salt.

Add the spaghetti to the boiling water in the pot. Stir for the first 30 seconds so the noodles do not stick together, then cook until tender with a little firmness in the center, about 9 to 11 minutes or according to the package.

Set a large skillet over medium heat and add the olive oil.

Put the sliced garlic and drained capers into the skillet. Cook, stirring often, until the garlic smells fragrant and just starts to turn pale gold, 30 to 60 seconds.

Add the drained cannellini beans to the skillet. Stir for 2 minutes so the beans are coated in the oil and warmed through.

Add the flaked tuna to the skillet. Stir very gently for about 1 minute so the tuna warms without breaking into tiny pieces.

Add the lemon zest and 1/2 cup of the pasta cooking water to the skillet. Let it bubble for 1 minute to make a light sauce, then lower the heat to low.