For the dressing, whisk together all ingredients in a small bowl.
For the greens beans, bring a large saucepan of salted water to a boil over high heat. Add the green beans and cook until tender-crisp, about 4 minutes.
Drain and immediately plunge the green beans into a bowl of ice water to stop the cooking and maintain the color of the beans.
In a large bowl, gently combine the green beans and tomatoes.
Add dressing to taste (you may not need all of the dressing).