For the schnitzel: Add the flour to a shallow dish and season with the seasoning salt and a pinch of salt and pepper. Whisk together the milk and eggs in a separate shallow dish. Add the breadcrumbs and parsley to a third shallow dish.
Heat the olive oil and butter in a large cast-iron skillet over medium-high heat.
Season the pork chops with salt and pepper. Bread the pork by coating the chops lightly in the seasoned flour, then dipping them in the egg mixture. Next, coat the chops in the breadcrumbs. You can use your fingertips to really press the breadcrumbs onto the pork, which will help the breading stay on while frying.
Carefully lay the pork chops in the skillet, cooking until golden and cooked through, 2 to 3 minutes per side. Transfer to a paper towel-lined plate to drain slightly and squeeze over the lemon.
For the cabbage. Meanwhile, heat the olive oil in a large skillet over medium-high heat. Add the red onion and fennel and mustard seeds and cook, stirring frequently, 2 to 3 minutes, being careful as the seeds might pop slightly during cooking. Add the cabbage, apple cider, vinegar and honey and cook until the cabbage is softened and the liquid is reduced slightly, 4 to 5 minutes.
For the sandwiches: Spread a heaping teaspoon each of mayo and mustard on both halves of each roll. Top the bottom half of each roll with 2 lettuce leaves, then top with a piece of schnitzel and some warm cabbage. Shingle over some slices of apple, then top with the other half of the roll. Serve with salt and vinegar potato chips.