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 preparation surface.
03 - Add cheddar slice to 4 bread slices. Top with BBQ chicken, onion slices, jalapeños, mozzarella slice, and another cheddar slice. Complete with second bread slice, buttered side facing outward.
04 - Heat skillet or griddle over medium heat. Cook sandwiches 3-4 minutes per side, pressing gently, until golden brown and cheese melts completely.
05 - Cut sandwiches diagonally in half and serve immediately while hot.