01 - Toss shredded chicken with BBQ sauce in a medium bowl until evenly coated.
02 - Butter one side of each bread slice. Place buttered side down on work surface.
03 - Place 1 cheddar slice on 4 bread slices. Top with BBQ chicken, red onion slices, jalapeños if desired, mozzarella slice, and another cheddar slice. Cover with remaining bread, buttered side facing outward.
04 - Heat large skillet or griddle over medium heat. Cook sandwiches 3-4 minutes per side, pressing gently, until golden brown and cheese is melted.
05 - Cut sandwiches in half and serve hot.