Whisk together the dressing ingredients in a saucepan. Heat to dissolve sugar & set aside to cool.
Trim green beans. Blanch by boiling for 2 minutes, then plunging into a bowl of ice water.
Mix the green beans with all of the remaining ingredients, except for the tomatoes. Toss with dressing, cover and refrigerate for several hours or overnight.
Before serving, bring to room temperature, add tomatoes, and stir to coat before serving.