Place the bacon in a large, deep skillet, and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain the bacon slice on a paper towel-lined plate. Let cool and crumble bacon. Reserve 1 teaspoon of bacon drippings.
Place a steamer insert into a saucepan, and fill with water to just below the bottom of the steamer. Cover, and bring the water to a boil over high heat. Add the green beans, recover, and steam until just tender, 3 minutes.
Whisk together olive oil, Dijon-style mustard, vinegar, bacon drippings, and shallot in a bowl. Toss hot, steamed green beans in a bowl with the dressing and crumbled bacon, and serve.