Make a dredging station: Add flour to a large shallow Entrée Bowl or Pie Dish and season with ½ tsp. salt and a few grinds of pepper. Stir together using a fork. Beat eggs, garlic powder, Italian seasoning, and ½ teaspoon salt together in another bowl. Add panko and ¼ cup parmesan to a third bowl.

Working with 1 cutlet at a time, dredge cutlets in flour, knocking off excess. Dip into egg mixture, allowing excess to drip back into dish. Add to panko mixture, pressing to adhere, making sure the cutlets are completely coated. Transfer chicken to a Sheet Pan and chill at least 20 minutes and up to 8 hours.

Combine mozzarella and Parmesan in a large bowl and set aside.

Fill a Stainless Clad Roasting Pan or large Dutch Oven with vegetable oil to a depth of ½ inch and heat over medium-high to 400F (place roasting pan over 2 burners). Working in batches if necessary, fry each cutlet until golden brown, about 2 minutes per side, until cooked through and internal temperature is 165F. Transfer to a Sheet Pan Rack set over a Sheet Pan and season with salt.

Meanwhile, heat broiler to high. Slice loaf in half lengthwise, place both halves cut side up on a Sheet Tray, and brush lightly with oil. Broil, watching closely, until toasted, about 2 minutes. Rub the toasted sides with the cut side of the garlic.

Set top half of loaf aside. Spoon ¾ cup marinara sauce on to the bottom half only. Shingle cutlets on top of marinara. Top with remaining ¾ cup marinara, allowing some of the crispy chicken to remain uncoated. Top sauce with the mozzarella mixture. Broil until cheese is melted and golden brown in spots, watching carefully, 2–5 minutes.. 

Top with additional Parmesan and parsley, if desired. Close sandwich and slice crosswise to serve.