Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease it with olive oil.
Place each chicken breast between two pieces of plastic wrap. Using a meat mallet or rolling pin, gently pound the chicken to an even thickness, about 1.0 inches thick.
In a shallow bowl, mix the breadcrumbs, grated Parmesan cheese, garlic powder, oregano, basil, salt, and pepper. In another bowl, whisk the egg. Dip each chicken breast into the egg, allowing any excess to drip off, then coat it with the breadcrumb mixture.
Place the coated chicken breasts on the prepared baking sheet. Lightly spray or drizzle olive oil over the tops. Bake in the preheated oven for about 20 minutes, or until the chicken is cooked through.
In the last 5 minutes of baking, remove the baking sheet from the oven. Spoon marinara sauce generously over each chicken breast, then sprinkle the shredded mozzarella cheese on top. Return to the oven and bake for an additional 5.0-7.0 minutes.
Lightly toast the hoagie rolls in the oven if desired. Once the chicken is ready, place each piece of cheesy chicken onto a roll, add fresh basil leaves for garnish, and drizzle with extra marinara if you like.
Close the sandwich and serve immediately while warm.