1. start by boiling a large pot of salted water for the pasta when the water for the pasta comes to a boil. cook until just underdone. 2. Remove ¼ cup of the cooking water and set aside before draining. 3. Meanwhile, heat the olive oil in a medium skillet over medium heat and add the onion and cook until translucent. add the garlic. cook, stirring, just until fragrant, and add the tomatoes. 4. Add the parsley and mix together. 5. Season to taste with salt and add pepper and the red pepper flakes if using. 6. Stir in the olives, and the tuna bring the sauce to a boil, cover, and simmer for 10 to 15 minutes while the pasta cooks. 7. Add the pasta, coat with the sauce, and cook until the pasta is done adding the reserved pasta water to loosen if necessary. taste for seasoning and add more salt as needed before serving.