Cook bacon in a large skillet over medium heat, turning once, until crisp, 5 to 7 minutes. Drain on a paper towel. Crumble.dd onion and salt to the drippings in the pan. Cook over medium heat, stirring often, until tender and browned, about 3 minutes. Add water and mustard and scrape up any browned bits. Add Brussels sprouts and cook, stirring often, until tender, 4 to 6 minutes. Stir in vinegar and top with the crumbled bacon.