In a large bowl, combine the cannellini beans, kidney beans, garbanzo beans, cherry tomatoes, red onion, pepperoncini, black olives, and parsley.
In a small bowl, whisk together the red wine vinegar, olive oil, oregano, salt, and black pepper.
Pour the dressing over the bean mixture and toss gently to coat.
Refrigerate for at least 30 minutes to allow the flavors to meld.
Serve chilled or at room temperature.