1. Bring a large pot of salted water to boil over high heat. Add pasta and cook until almost tender, about 8 minutes. Add green beans to pot and continue to boil until beans and pasta are both tender, about 2 minutes longer. Drain, reserving 1/4 cup cooking water. Run pasta and beans under cold water and drain again. Set pasta and green beans aside.
2. In a large bowl, whisk together oil, vinegar and salt. Stir in tuna, tomatoes, olives, parsley and capers.
3. Add pasta and green beans to bowl. Stir, adding reserved cooking water to moisten as necessary, and serve.