Preheat oven to 350 degrees. Place 4 slices of bread on a work surface and spread each slice with some mustard. Add 2 slices of the chicken, followed be a slice of cheese and another slice of bread. Repeat for a second layer with the mustard, chicken and cheese, and end with a slice of bread.
Add the salt and pepper to the flour for first dipping bowl. Whisk the eggs and milk until smooth for second dipping bowl. Breadcrumbs are third dipping bowl.
Coat sandwiches lightly in flour on all sides, then dip each lightly into eggs, then into breadcrumbs, covering all sides, keeping the egg batter from inside the sandwich.
Spray each sandwich with cooking spray. Place each on a baking sheet and bake for 12 minutes or until golden. Serve with strawberry preserves if desired.