01 - Cook turkey bacon in skillet over medium heat until crispy, approximately 4-5 minutes per side. Transfer to paper towel-lined plate to drain excess grease.
02 - Toast all bread slices until golden brown. Spread each slice lightly with softened butter while warm for enhanced flavor and texture.
03 - Spread mayonnaise and Dijon mustard evenly on one side of each toasted bread slice, ensuring full coverage to the edges.
04 - Place first bread slice mayo-side up. Layer with half the lettuce leaves, followed by half the sliced turkey breast and tomato slices. Season with salt and pepper.
05 - Place second bread slice mayo-side down onto stack. Spread mayo on top side. Add remaining turkey bacon, extra lettuce, tomatoes, and onion slices if desired.
06 - Top with third bread slice mayo-side down. Press gently to compact layers. Secure with toothpicks at each corner and slice diagonally into halves or quarters.
07 - Repeat assembly process for second sandwich. Serve immediately while bread remains crispy and vegetables fresh.