Make your slaw: Quarter, core, and thinly slice your cabbage. If slices are long, I cut them into 1 to 2-inch lengths, so the slaw doesn’t end up too cumbersome to pile on a sandwich. Place in a large bowl and pour 1/3 cup mop over, toss to combine. Add mayonnaise and mix well to combine. Season with salt and more pepper, if you wish, and taste, add more mop or mayo if needed. Refrigerate until ready to eat.