HEAT oven to 400ºF.
PREPARE stuffing mix as directed on package.
PLACE chicken in 13x9-inch baking dish sprayed with cooking spray; cover with ham. Mix soup and mustard; spoon over chicken. Top with stuffing.
BAKE 25 min. or until chicken is done (165°F). Top with cheese; bake 5 min. or until cheese is melted.