Prepare the seitan: Preheat the oven to 375°F. Whisk together all the mojo ingredients except the seitan in a ceramic or glass 7 x 11-inch baking pan. Add the seitan strips and toss to coat with the marinade. Roast for 10 minutes, then flip the slices over once, until the edges are lightly browned and some juicy marinade still remains (don’t overbake!). Remove from the oven and set aside to cool.
Assemble the sandwiches: Slice each roll or piece of bread in half horizontally and generously spread both halves with the butter or brush with olive oil. On the bottom half of each roll, spread a thick layer of mustard, a few slices of pickle, two slices of the ham, and one-fourth of the seitan slices, and top with two slices of the cheese.
Dab a little of the remaining marinade on the cut side of the other half of the roll, then place atop the lower half of the sandwich. Brush the outsides of the sandwich with a little more olive oil or spread with the butter.
Preheat a 10- to 12-inch cast-iron pan over medium heat. Gently transfer two sandwiches to the pan, then top with something heavy and heatproof, such as another cast-iron pan or a brick covered with several layers of heavy-duty aluminum foil. Grill the sandwich for 3 to 4 minutes, watching carefully to prevent the bread from burning; if necessary, lower the heat slightly as the sandwich cooks.
When the bread looks toasted, remove the pan/brick and use a wide spatula to carefully flip each sandwich. Press again with the weight and cook for another 3 minutes or so, until the cheese is hot and melty.
Remove the weight, transfer each sandwich to a cutting board, and slice diagonally with a serrated knife. Serve hot!