Cut 2 boneless, skinless chicken breast halves (6 - 8 ounces each) in half horizontally almost all the way through leaving far edge intact and open up like a book. Cover with Saran™ brand plastic wrap and pound opened breasts gently to even thickness (about 1/4 inch), being careful not to tear chicken. Sprinkle open (cut-side) of chicken with salt and pepper to taste.
Cut 1 slice of Swiss cheese (about 1 ounce) in half. Wrap each half of cheese in 1 slice of deli ham (about 1/2 ounce each), folding ham over cheese on all sides to fully surround cheese. Place one ham and cheese bundle on each chicken breast.
Put stuffed chicken breasts into Ziploc® brand Zip 'n Steam® Medium or Large bag, with thickest part of chicken breasts toward outer edge of bag.
Seal bag and place in microwave. Cook on full power for 5 - 5 1/2 minutes, until chicken is cooked through, with no trace of pink. If needed, continue microwaving at 30-second intervals until chicken is done.
Allow bag to stand 1 minute before handling. Carefully open bag. Use spatula to remove chicken from bag. Serve with mustard sauce.