01 - Combine cooked pulled pork and barbecue sauce in a small bowl until evenly coated. Warm the mixture gently in a skillet or microwave if the pork is cold.
02 - Arrange bread slices on a work surface. Spread softened butter on one side of each slice. On the unbuttered side of 4 slices, layer 1 slice of cheddar cheese, a generous portion of pulled pork mixture, and, if desired, red onions and pickled jalapeños. Top each with a second slice of cheddar cheese and cover with remaining bread, buttered side facing outward.
03 - Preheat a large skillet or griddle over medium heat. Place the assembled sandwiches onto the hot surface and cook for 3 to 4 minutes per side, pressing gently with a spatula, until the bread is golden brown and the cheese is fully melted.
04 - Transfer sandwiches to a cutting board. Let rest for 1 minute before slicing. Serve hot.