- Preheat the oven to 375ºF (190ºC). Chop the pretzels into small pieces; discard fine pretzel dust. Toss the pieces with the Parmesan and butter; set aside. Cut each chicken breast through the center, leaving one side intact, so it opens like a book. Stir the mustard with the green onion, salt and pepper. Brush all over the inside of the chicken. Place a slice of ham in the centre of each piece; fold over to enclose.
- Brush the tops of the chicken with egg and sprinkle with the pretzel mixture over top; press lightly to adhere. Arrange chicken on a foil-lined baking sheet. Bake for 25 minutes or until an instant-read thermometer registers 165ºF (74ºC) when inserted into the center of the largest chicken breast.
Serve with additional honey mustard for dipping.