Place beans in saucepan and cover with water,bring to a boil.Cook,uncovered for 8 to 10 minutes,drain and set aside.
In a skillet,cook bacon over medium heat until crisp.Remove to paper towel. Drain,reserving 1 Tablespoon drippings.
In the same skillet,saute onion on drippings until tender.
In a small bowl,combine the cornstarch, mustard,and water until smooth. Stir in onion.Bring to a boil cook and stir for 1 to 2 minutes or until thickened.Stir in brown sugar and vinegar.Add the beans,heat through, top with bacon.