01 - Cook turkey bacon in a skillet over medium heat until crispy, about 4-5 minutes per side. Transfer to a 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 if desired for extra flavor.
03 - Spread mayonnaise and Dijon mustard evenly on one side of each toasted bread slice. Ensure even coverage for consistent flavor distribution.
04 - Place one bread slice mayo-side up. Layer with half the lettuce, followed by half the sliced turkey breast and several tomato slices. Season lightly with salt and pepper.
05 - Place second bread slice mayo-side down onto stack. Spread mayo on top side. Add half the cooked turkey bacon, additional lettuce and tomato as desired, and onion slices if using.
06 - Finish with third bread slice mayo-side down. Press down gently to compress layers. Secure with toothpicks at each corner and slice diagonally into halves or quarters.
07 - Assemble second sandwich following same steps. Serve immediately while bread remains crispy and bacon stays warm.