Heat panini press or large skillet over medium heat.
Combine the creamy horseradish and mayonnaise together in a small bowl until fully incorporated.
To assemble sandwiches, spread softened butter on outside slices of bread.On the inside of a slice spread the mayonnaise mixture. Add half of the cheese, followed by the arugula and then pulled pork.Top it with remaining cheese and slice of bread with buttered side up.
Cook sandwiches until golden brown on both sides.