Cook the pasta according to the package directions.
Meanwhile, heat 3 T. of the oil in a large skillet over medium-low heat. Add the garlic and cook until softened, about 2 minutes. Add the capers and olives and cook for 3 minutes. Stir in the parsley and cook until wilted, about 1 minute. Remove from heat.
Add the lemon juice, pepper, and the remaining oil.
Drain the pasta, rinse under cold water, and top with the tuna and olive vinaigrette.