In a large saucepan, cook bacon over medium heat until crisp, stirring occasionally; drain drippings. Add vegetables, seasonings and broth; bring to a boil. Reduce heat; simmer, covered, until potatoes are tender, 10-15 minutes.

Mix flour and milk until smooth; stir into soup. Bring to a boil, stirring constantly; cook and stir until thickened, about 2 minutes. Stir in cheese until melted. If desired, serve with green onions.