Bring a large pot of salted water to a boil. Add the pasta and cook according to package instructions until al dente, typically around 8-10 minutes.
While the pasta cooks, prepare the other ingredients. Drain the tuna and set aside. Chop the cherry tomatoes, cucumber, and red onion.
Once the pasta is cooked, drain it in a colander and rinse under cold water to stop the cooking process. Let it cool for a few minutes.
In a large mixing bowl, combine the cooled pasta with drained tuna, cherry tomatoes, cucumber, red onion, and sweet corn.
In a separate small bowl, whisk together the olive oil, lemon juice, dried oregano, salt, and pepper.
Pour the dressing over the pasta mixture and toss gently until everything is well coated.
Taste and adjust seasoning if necessary. Garnish with fresh parsley if desired.
Serve immediately or chill in the refrigerator for about 30 minutes for a colder salad.