At home, I like to jazz things up by adding a mayonnaise spiked with Peppadews, those miniature red peppers from South Africa that are pickled to sweet-and-sour perfection to my chicken sandwich. If you can't find them, substitute your favorite bread-and-butter pickle.
Pour 1 tablespoon of the oil into a medium skillet over medium heat. When it starts to shimmer, add the red pepper flakes and cook, stirring, for a minute or 2. Add the broccoli rabe and sauté until the broccoli rabe is tender, 4-5 minutes. Use a slotted spoon to transfer the broccoli rabe and red pepper flakes to a plate or bowl.
In a small bowl, stir together the peppadew peppers and mayonnaise.
Lay the chicken between 2 large pieces of plastic wrap on your work surface, and pound it to a thickness of about ¼ inch. Season it generously on all sides with salt and pepper.
In a shallow bowl, whisk the egg to combine. Spread the panko crumbs onto a plate. Dip the chicken breast in the egg and then dredge it in the panko crumbs, turning it and patting them on with your hands to coat the chicken well.
Pour the remaining 2 tablespoons of oil into the skillet over medium heat. When it starts to shimmer, lay the chicken cutlet in the pan and let it cook undisturbed until it is golden brown on the bottom, 2-3 minutes. Use tongs to turn the cutlet over, then lay the provolone pieces on the cooked side of the chicken, overlapping slightly, and cook until the bottom is golden brown and the chicken is cooked through, 2-3 minutes. Transfer the chicken to a serving plate.
To assemble the sandwich, place the 2 roll halves on the serving plate. Spread one slice with the peppadew mayonnaise, then top with the chicken cutlet, broccoli rabe, and remaining roll half, and eat.