Stir together coleslaw mix, 2 Tbsp. Thousand Island dressing, vinegar, and pepper in a medium bowl.
Stir together spicy brown mustard and remaining 3 Tbsp. Thousand Island dressing; spread mixture evenly on 1 side of bread slices. Top 2 bread slices evenly with beef; top each with half of apple slices and 1 cheese slice. Divide slaw mixture evenly over cheese. Top with remaining bread slices, dressing mixture sides down. Brush both sides of sandwiches evenly with melted butter.
Cook sandwiches in a large lightly greased nonstick skillet over medium-high heat 2 minutes on each side or until golden. Serve immediately.