In a large bowl, whisk the first 4 ingredients and 1 T. of the oil; set aside. In a nonstick skillet, saute chicken in remaining oil over medium heat until juices run clear. Add to vinaigrette and toss to coat.
Place green beans in a steamer basket in a saucepan over 1-in. of water. Bring to a boil; cover and steam for 5-10 minutes or until crisp tender. Add to chicken mixture. Add tomatoes and toss to coat. Cover and refrigerate for at least 1 hour. Toss again before serving.