Heat oil in a grill pan or flattop grill. When hot, add plantains rounds. Cook until browned on one side and flip, turning down the heat if necessary to ensure that plantain is cooked through.
Remove rounds and flatten them with a mallet or cast iron pan. Return plantains to the grill for a second grill to crisp the outer edges. Remove and drain on paper towels.
Stack each sandwich with a plantain on the bottom, topped by equal portions of pork, and one square of cheese. Place under a broiler for approximately 30 seconds or until cheese melts. Top with one pickled cucumber, pickled red onions, a second plantain round, and cilantro.
Repeat until you have 12 mini sandwiches; serve immediately.