Mix maple syrup and apple pie spice. Set aside. Butter 1 side of each of the bread slices. Layer 2 slices of cheese and 4 slices of apple on each of 4 bread slices with buttered side down. Sprinkle with chopped bacon then drizzle with maple syrup mixture. Top with remaining bread slices with buttered side up.
Place sandwiches in large skillet or griddle on medium-low heat. Cook 3 to 4 minutes per side or until bread is browned and cheese is melted. Cook in batches if necessary.