If using chicken, cut into cutlets, salt on both sides for 10 minutes, pat dry, and place cutlets between two pieces of parchment or plastic wrap. Using a kitchen mallet or rolling pin, pound meat to even ¼-inch-thick slices. Mix together buttermilk, garlic, kosher salt, and pepper and place chicken into the mixture. Allow to marinate for 30 minutes on the counter or up to overnight in the fridge. If using eggplant for one or both halves of the casserole, wash and slice into ¼-inch-thick slices, then sprinkle salt on each slice and wait 10-20 minutes before drying with paper towels. Note that the eggplant should not be marinated.

Place flour, eggs and panko into three wide, shallow bowls. Dip a piece in flour, then eggs, then coat with panko. Repeat until all the chicken/eggplant is coated.

Fill a large skillet with ½-inch oil. Place over medium-high heat. When oil is hot, fry cutlets in batches, turning halfway through, until golden brown. Transfer to a paper towel-lined plate. You could instead, should you so choose, air fry them at 350 degrees for 18 minutes, turning once.

Heat oven to 400 degrees. Spoon a thin layer of sauce over the bottom of a 9-by-13-inch baking pan. Sprinkle one-third of the Parmesan over sauce. Place half of the cutlets over the Parmesan and top with half the mozzarella pieces. Top with half the remaining sauce, sprinkle with another third of the Parmesan, and repeat layering, ending with a final layer of sauce and Parmesan.

Transfer pan to oven and bake until cheese is golden and casserole is bubbling, about 40 minutes. Let cool a few minutes before serving.

While the casserole cooks, boil penne rigate (or other pasta) according to its instructions. Serve the pasta with the casserole on top, and sprinkle additional Parmesan as desired.