In a bowl, toss the cooked chicken with the barbecue sauce until evenly coated. Set aside.
Butter one side of each slice of bread. On the unbuttered side of two slices, layer half the shredded cheese, followed by the BBQ chicken, and then the remaining cheese. Top with the second slice of bread, buttered side facing out.
Heat a nonstick skillet or griddle over medium heat. Place the sandwiches in the pan and cook for about 3–4 minutes per side, or until the bread is golden brown and the cheese is melted.
Remove from the skillet, let rest for a minute, then slice in half and serve hot. Pair with chips, coleslaw, or a side salad.