Combine margarine, poppy seeds, Worcestershire sauce, mustard and onion. Wisk until mixed thoroughly.
Split rolls lengthwise. Spread about two-thirds of the mixture on bottom halves of the rolls; then place ham slices and cheese slices on top of this.
Replace tops of rolls and spread remaining mixture on the tops.
Cover with foil; heat at 400 degrees for about 10 minutes or until cheese is melted.