In 12-inch skillet, cook bacon over medium heat, turning occasionally, until browned and crispy. Remove from skillet, reserving fat in skillet. Drain bacon on paper towel. In same skillet, cook onion in bacon fat over medium heat 4 to 5 minutes, stirring frequently, until tender.
Add potato, onion, broth, salt and pepper to 4qt. slow cooker. Cover and cook on low setting for 6-7 hours.
In small bowl, beat flour and half-and-half with wire whisk until well blended; stir into soup. Increase heat setting to High. Cover; cook about 30 minutes longer or until thickened. Stir in 2 cups cheese until well melted. Spoon into bowls and top with crumbled bacon, a bit more cheese and green onion.