Cook green beans according to package directions. Meanwhile, in a Dutch oven, saute onion in butter until tender. Remove from the heat; whisk in the flour, salt, paprika, Worcestershire sauce and mustard until blended.
Gradually stir in milk. Bring to a boil; cook and stir for 2 minutes or until thickened and bubbly. Remove from the heat; stir in cheese.
Drain beans; gently fold into cheese sauce. Transfer to a large serving bowl. Toss bread crumbs and butter; sprinkle over beans.