Creating a Chicken Parmesan Sandwich involves several straightforward steps. Follow these instructions for a successful outcome:

1. Preheat Oven: Preheat your oven to 400°F (200°C) to prepare for baking the chicken.
2. Prepare Chicken: Flatten the chicken breasts to an even thickness using a meat mallet. This ensures even cooking.
3. Set Up Breading Station: In three separate bowls, place flour in one, beaten eggs in another, and breadcrumbs mixed with garlic powder, oregano, salt, and pepper in the third.
4. Bread the Chicken: Dredge each chicken breast in flour, shaking off the excess. Then dip into the beaten eggs and finally coat with breadcrumbs, pressing gently to adhere.
5. Heat Oil: In a large skillet, heat olive oil over medium heat. Once hot, add the breaded chicken breasts.
6. Cook Chicken: Cook for 4-5 minutes on each side until golden brown and cooked through. Use a meat thermometer to ensure the internal temperature reaches 165°F (75°C).
7. Prepare for Baking: Transfer the cooked chicken to a baking dish. Top each piece with marinara sauce and a generous sprinkle of mozzarella and Parmesan cheese.
8. Bake: Place in the preheated oven and bake for 10-12 minutes, or until the cheese is bubbly and golden.
9. Toast the Bread: While the chicken bakes, lightly toast the slices of Italian bread or sub rolls in the oven until golden.
10. Assemble the Sandwich: Remove the chicken from the oven. Place one chicken piece on each slice of toasted bread. Add additional marinara sauce on top if desired.
11. Garnish: Optionally, add fresh basil leaves for a pop of color and flavor.
12. Serve: Close the sandwich with the other slice of bread and serve hot.

These steps will guide you in creating a delicious Chicken Parmesan Sandwich that is sure to satisfy.