Boil water in a large pot and cook that pasta for 7-9 minutes. Rinse it in a colander under cold water and then let it drain.
While the pasta cooks, make the dressing. In a small bowl, whisk together the olive oil, vinegar, mustard, garlic powder, oregano, and salt and pepper.
In a large bowl, add the drained pasta, tuna (break it into chunks first), tomatoes, cucumber, bell pepper, onion, parsley, and olives. Pour the dressing over the pasta and vegetables and toss to combine everything.