In a large mixing bowl, combine the black beans, kidney beans, and chickpeas.

Add the cherry tomatoes, cucumber, and red onion to the bowl.

In a small bowl, whisk together the olive oil, red wine vinegar, minced garlic, salt, black pepper, and dried oregano.

Pour the dressing over the bean and vegetable mixture and toss gently to combine.

Serve immediately or refrigerate for 30 minutes to allow flavors to meld.