Cook the pasta in a large pot of boiling salted water until tender but still firm to the bite, about 8 minutes.
Meanwhile, combine the tomato sauce, tuna, capers, and lemon peel in a heavy large skillet. Using a fork, break the tuna into chunks. Simmer to blend the flavors, about 5 minutes. Season with salt and pepper, to taste.
Drain the pasta, reserving 1 cup of the cooking liquid. Add the pasta to the sauce and toss to coat. Toss the pasta with enough reserved cooking liquid to moisten. Stir in the parsley and serve.
Simple Tomato Sauce:
In a large casserole pot, heat oil over medium high heat. Add onion and garlic and saute until soft and translucent, about 2 minutes. Add celery and carrots and season with salt and pepper. Saute until all the vegetables are soft, about 5 minutes. Add tomatoes, basil, and bay leaves and simmer covered on low heat for 1 hour or until thick. Remove bay leaves and check for seasoning. If sauce still tastes acidic, add unsalted butter, 1 tablespoon at a time to round out the flavors.
Add half the tomato sauce into the bowl of a food processor. Process until smooth. Continue with remaining tomato sauce.
If not using all the sauce, allow it to cool completely and pour 1 to 2 cup portions into freezer plastic bags. This will freeze up to 6 months.