1. Bring a pot of salted water to boil. Add pasta and cook until tender, about 12 minutes, or as package label directs.
2. In a bowl, whisk oil, lemon zest and juice and 1/2 tsp. salt. Drain pasta; add to bowl with dressing. Add tomatoes, tuna, olives, onion and parsley and toss well. Let cool to room temperature, season with salt and pepper, if desired, and serve.