Bring a medium pot of salted water to a boil. Cook green beans for about 5 minutes; then drain and run under cold water.
Whisk together shallot, garlic, mustard, vinegar, olive oil, salt and pepper.
In a large bowl, toss green beans, lettuce and blue cheese with dressing to coat. Transfer to a serving dish or bowl and top with chopped nuts, tomatoes and more crumbled blue cheese, if desired.