Heat oven to 375°F. Line cookie sheet with foil. Place chicken breasts flat on cutting surface. With knife parallel to cutting surface, cut lengthwise slit in each chicken breast, forming a pocket, keeping other 3 sides intact. Stuff each chicken breast with pepperoni and mozzarella cheese, pressing edges of each chicken breast to seal.
Place chicken breasts on cookie sheet. Spray tops of chicken with cooking spray. Sprinkle bread crumbs evenly over chicken breasts. Spray with cooking spray.
Bake 20 to 25 minutes or until juice of chicken is clear when center of thickest part is cut (at least 165°F). Serve chicken with salad greens tossed with dressing.
Place the cheese stick halves in the freezer 15 to 20 minutes.
While the cheese is freezing, place the panko on a baking sheet and lightly toast in the oven. Remove from heat and combine with the garlic salt and Italian seasoning in a small mixing bowl. Set aside.
Place the egg and flour in a small, shallow bowl. Set aside.
Remove from the freezer and dredge in the flour. Dip the cheese into the egg mixture and then the panko mixture; making sure to press the cheese firmly into the panko.
Place the cheese on a baking rack placed on top of a sheet pan. Continue with remaining cheese, flour, egg, and panko.
Bake at 400 for 8 to 10 minutes or until the coating is crisp and the cheese is heated through. Remove from heat and cool slightly before serving with the tomato pesto or other, favorite dipping sauce.