01 - Cook the turkey bacon in a skillet over medium heat until crisp, about 6-8 minutes. Drain on paper towels.
02 - Toast the bread slices until golden brown.
03 - Spread mayonnaise (and Dijon mustard, if using) evenly on one side of each bread slice.
04 - Place a slice of bread, mayo side up, on a plate. Layer with lettuce, sliced turkey breast, and a slice of cheese.
05 - Top with a second slice of bread, mayo side down. Spread mayo on the top side, then layer with turkey bacon, tomato slices, and avocado (if using).
06 - Finish with the third slice of bread, mayo side down. Gently press down, then use a sharp knife to cut the sandwich diagonally into halves or quarters. Secure each section with a toothpick if desired.
07 - Serve immediately with your favorite side.