Cook asparagus as label directs; drain.
In small saucepan, melt butter; stir in flour, then milk; cook, stirring constantly, until thickened.
Stir in cheese until melted.
Place toast on cookie sheet.
Top with asparagus spears, then with turkey slices and drained mushrooms.
Spoon on cheese sauce.
Broil 3 to 5 minutes or until golden.