Bring a small pot of water to a boil. Add the green beans and cook for 3-4 minutes, or until bright green and tender crisp. Drain and immediately run under cold water to stop the cooking process.
In a medium bowl, combine the green beans, chickpeas, tuna, tomatoes, olives, and celery. Mix well.
In a small bowl, whisk together the lemon juice, mustard, shallot, and olive oil. Pour the dressing over the salad and mix to combine. Season to taste with salt and pepper. Serve immediately, or refrigerate.