01 - Evenly distribute salt and freshly ground black pepper over both sides of the sliced cooked chicken breasts, ensuring full coverage for optimal flavor penetration.
02 - Arrange bacon slices in a cold skillet and place over medium heat. Cook for 6-8 minutes, turning occasionally, until strips reach desired crispiness. Transfer to paper towels to drain excess grease.
03 - Lightly spread softened butter on one side of each bread slice. Toast in a toaster, under a broiler, or in a skillet until golden brown and slightly crisp. Set aside to cool for 1 minute before assembly.
04 - Select three toasted bread slices per sandwich. Generously spread mayonnaise (and mustard if desired) on one side of each slice, ensuring even coverage to the edges.
05 - On the first bread slice, mayonnaise-side up, arrange 2 romaine lettuce leaves, followed by 2-3 tomato slices, and half of the seasoned chicken. Press gently to compact ingredients.
06 - Place a second bread slice, mayonnaise-side down, over the chicken layer. Add 2 more lettuce leaves, additional tomato slices, and 2 crispy bacon strips, breaking them to fit if necessary.
07 - Position the third bread slice, mayonnaise-side down, atop the bacon layer to seal the triple-decker structure. Press firmly but gently to stabilize the sandwich.
08 - Insert decorative toothpicks through opposite corners of each sandwich, approximately 1 inch from each edge, to prevent sliding during serving.
09 - Using a sharp serrated knife, slice each assembled sandwich diagonally from corner to corner, creating two triangular halves. For appetizer portions, quarter each sandwich with a second diagonal cut.
10 - Repeat the layering and assembly process for the remaining three sandwiches using the remaining ingredients. Serve immediately on chilled plates with accompaniments of choice.