Fry the plantain: Heat oil in a medium frying pan over medium heat. Once oil is shimmering, add plantain slices in a single layer (you may need to do this in batches). Fry until browned on one side, about 2 minutes, flip and repeat on the other side. Transfer to a paper towel-lined plate and sprinkle with salt. 

Layer it up! Slice the rolls in half. Lay a couple slices of avocado on each half, sprinkle with salt and pepper. Spread some of the chopped chipotles over the avocado slices. Lay a couple of plantain pieces on top then evenly distribute the cheese, Papalo, and onion slices among the sandwiches. Place the other side of the rolls on top and dig in!