Bring a large pot of salted water to a boil. Add the fresh green beans and blanch for 2 minutes until crisp-tender.
Immediately transfer the green beans to a bowl of ice water to cool, then drain well.
In a large mixing bowl, combine the blanched green beans, drained kidney beans, drained chickpeas, red onion, and parsley.
In a separate small bowl, whisk together the apple cider vinegar, olive oil, sugar, Dijon mustard, kosher salt, and black pepper until completely emulsified.
Pour the dressing over the bean mixture and toss gently to ensure all ingredients are evenly coated.
Cover and refrigerate for at least 1 hour to allow the flavors to meld. Toss well before serving.