Bring a medium pot of water to a boil over high heat. Season it with salt. Cook the green beans for 3 to 4 minutes, until crisp yet tender. Drain the green beans in a colander and rinse them under cold water until cool. Let dry.

In a large mixing bowl, combine the green beans, kidney beans, chickpeas, celery, and red onion.

In a medium bowl, whisk to combine the vinegar, sugar, salt, and pepper. While whisking, slowly add the olive oil, starting with a few drops and increasing to a slow stream to emulsify into the dressing.

Pour the dressing over the bean mixture and add the parsley. Mix well to combine. Let sit for 30 minutes before serving. Season with more salt and pepper to taste.