Meanwhile, in 10-inch skillet, cook bacon over medium-high heat 7 to 9 minutes, stirring frequently, until bacon is browned. Remove bacon to paper towel-lined plate. Drain all but 1 teaspoon bacon drippings. Decrease heat to medium. In same skillet, cook onion in 1 teaspoon bacon drippings 3 to 4 minutes, stirring frequently, until onion is tender. Stir bacon, onion and mustard into broccoli mixture; spread in baking dish.