01 - Evenly season the cooked chicken breast slices on both sides with salt and black pepper, ensuring thorough coverage for maximum flavor absorption.
02 - Arrange bacon slices in a cold skillet and place over medium heat. Cook until desired crispness is achieved, approximately 5-7 minutes per side. Transfer to paper towels to drain excess grease.
03 - Lightly butter one side of each bread slice. Toast in a skillet, toaster, or panini press until golden brown and crispy. Alternatively, use a toaster for a lighter preparation.
04 - Lay out three slices of toasted bread per sandwich. Generously spread mayonnaise (and Dijon mustard if using) on one side of each slice, ensuring complete edge-to-edge coverage.
05 - On the bottom slice, layer two romaine lettuce leaves followed by tomato slices. Arrange half the seasoned chicken pieces evenly across the vegetables, maintaining structural integrity for the next layer.
06 - Place the second bread slice, mayonnaise-side down, over the first layer. Add two more lettuce leaves, additional tomato slices, and two crispy bacon strips positioned perpendicular to the bread edge for easy eating.
07 - Top with the final bread slice, mayonnaise-side facing downward, creating a stable triple-decker structure. Press gently to settle ingredients without compressing excessively.
08 - Insert toothpicks at opposite diagonal corners to prevent sliding during cutting. Using a sharp serrated knife, slice each sandwich diagonally from corner to corner, creating two triangular halves or four quarters for smaller portions.
09 - Repeat the assembly process for remaining sandwiches. Serve immediately while bread retains crunchiness and bacon remains crisp. Accompany with pickles, coleslaw, or a simple green salad.