Melt margarine in same saucepan on medium-high heat; blend in flour. Cook 3 min., stirring constantly. Add broccoli mixture and mustard; mix well. Cook 4 to 5 min. or until mixture thickens and begins to boil, stirring occasionally. Add half-and-half, pepper and cheese; stir until blended. Cook 2 to 3 min. or until heated through, stirring occasionally.