In a medium bowl, combine the shredded chicken with the BBQ sauce. Mix well until the chicken is evenly coated.
Heat a skillet over medium heat.
Butter one side of each slice of bread using 1 tablespoon of butter per slice.
Place two slices of bread, buttered side down, in the skillet.
On each slice in the skillet, layer half of the shredded cheese, followed by an equal amount of the BBQ chicken mixture. Top with the remaining shredded cheese, then cover with the other slices of bread, buttered side up.
Cook for 3-4 minutes until the bottom is golden brown. Carefully flip the sandwiches using a spatula, and cook for an additional 3-4 minutes until the other side is golden brown and the cheese is melted.
Transfer the sandwiches to a cutting board. Let them rest for a minute before slicing in half.
Serve warm, and if desired, garnish with sliced pickles or jalapeños.