At a slight angle, cut 6 slits into each of the chicken breasts, making sure not to cut all the way through. You should leave roughly 1/4 inch unsliced. Brush the top of each chicken breast with 1 tablespoon of the mustard.
Mix together the breadcrumbs, butter, salt and pepper in a bowl. Sprinkle the breadcrumb mixture evenly over the chicken, using your hands to press the mixture into the mustard. Place a quarter piece of cheese and a half-moon piece of Canadian bacon into each of the slits in each chicken breast. Transfer the stuffed chicken breasts to a baking sheet.
Bake until the chicken is cooked through and the breadcrumbs are golden, 20 to 22 minutes. Serve warm with your favorite sides.
Freezing instructions: Once the uncooked chicken breasts are assembled, place 4 onto a wax paper-lined baking sheet; repeat with the remaining chicken breasts on a separate lined baking sheet. Transfer the baking sheets to the freezer until the chicken breasts are frozen through, at least 3 hours. Transfer the chicken breasts to 2 wax paper-lined foil pans. Label, date and freeze until ready to eat.
When ready to eat, preheat the oven to 425 degrees F. Bake the chicken breasts from frozen until the chicken is cooked through and the breadcrumbs are golden, about 40 minutes. Serve as directed above.