Place chicken breasts between two sheets of plastic wrap and pound to an even 1/2-inch thickness. Season with salt and pepper.
Set up a breading station: In a shallow dish, combine flour, garlic powder, oregano, salt, and pepper. In another dish, beat eggs. In a third dish, mix breadcrumbs and Parmesan cheese.
Dredge each chicken breast in flour mixture, then dip in egg, then coat with breadcrumb mixture, pressing firmly.
In a large skillet, heat oil over medium-high heat. Fry chicken cutlets for 3-4 minutes per side until golden brown and cooked through (internal temperature 165°F). Drain on paper towels.
Preheat broiler. Place split hoagie rolls cut-side up on a baking sheet and toast under broiler for 1-2 minutes until lightly golden.
Spoon a little marinara sauce onto the bottom half of each roll. Place a chicken cutlet on top, then spoon more sauce over the chicken. Top with mozzarella slices.
Broil sandwiches for 2-3 minutes until cheese is melted and bubbly. Garnish with fresh basil leaves and close sandwich. Serve immediately.
Tips
For extra crispiness, use panko breadcrumbs instead of regular.
Serve with extra marinara sauce on the side for dipping.
Leftover chicken can be reheated in a toaster oven to maintain crispness.