Cut the stem ends off the beans. Place in a microwave safe dish with about 3 tablespoons of water, cover loosely and cook on high 2 1/2 to 3 minutes, just until tender crisp. Drain and dump into a bowl of cold water. Drain again and pat dry.
In a large saute pan, over medium low heat, melt the butter until bubbling. Add the shallots and saute until golden and softened, about 4 minutes. Add the vermouth and turn the heat up to medium. Simmer for 1 to 2 minutes. Add the mustard seeds, sugar, tomatoes, mint, salt and pepper. Saute to soften, about 4 minutes.
Reduce the heat to low and add the blanched green beans. Toss to combine and heat through, about 4 to 5 minutes. Adjust seasoning. Serve immediately.