Bring a large pot of salted water to a boil. Add the green beans and cook them until they are bright green and crisp-tender, about 5 minutes (it might take longer if you use thicker beans).
Drain the beans and rinse them with cold water until they're chilled.
In a large bowl, whisk together the vinegar, oil, salt, and pepper.
Add the cold beans, sun dried tomatoes, and feta cheese; toss gently to coat all of the ingredients with the dressing. Serve cold.