Heat 1 tablespoon of olive oil in a skillet over medium heat. Once hot cook onion over medium-low heat until brown and caramelized. About 15 minutes.
Remove onions. Add pulled pork and remaining olive oil to the pan and cook until warmed through.
To assemble the sandwiches. Butter one side of each slice of bread. On the side that is not buttered place two slices of pepper jack cheese. Top with pulled pork and caramelized onions and one more slice of cheese. Top with another slice of bread, butter side out.
In the same skillet you cooked the onions in, cook the sandwiches over medium heat until the cheese has melted and bread is browned. Serve.