Bring a large pot of salted water to a full boil, and cook the paccheri pasta to al dente according to the packaging's manufacturing instructions.
Meanwhile, add one tablespoon of olive oil and the garlic to a large skillet. Cook the garlic over medium heat until it turns golden, then remove it and toss.
Add the cherry tomatoes, half of the fresh chopped parsley, and the olives to the skillet. Cook over medium heat until you hear and see the tomatoes bursting. Season with salt and pepper and stir. Add the cubed tuna, gently stir, and cook until the tuna is cooked through.
Before draining the pasta, save a cup of the cooking water. Drain the pasta and return it to the pot. Pour in the tuna-tomato sauce, add a splash of the reserved pasta water if needed to loosen it up, and drizzle in the remaining tablespoon of olive oil. Toss gently to combine.
While cutting the tuna, ensure that all the pieces are the same. This will help ensure an even cooking time.
Do not worry if your pasta is not fully cooked or al dente. Once added with the tomatoes and tuna, it will continue cooking to the desired consistency.
Giangi's Kitchen provides nutritional information, but these figures should be considered estimates, as a registered dietician does not calculate them.