Fill medium saucepan with water and set to boil. Add green beans to boiling water, and boil for 5 minutes.
Drain green beans in a colander and run cold water over them to stop the cooking process.
Meanwhile, add bacon and onion to large non-stick skillet. Sauté on low-medium heat for 5 minutes, stirring frequently. Add garlic, mustard and drained green beans to skillet.
Continue to sauté and stir occasionally for 2-3 minutes until the green beans are tender. Serve.