01 - Cook turkey bacon in a skillet over medium heat until crisp, approximately 6 to 8 minutes. Drain on paper towels to remove excess grease.
02 - Toast bread slices in a toaster until golden brown and crispy.
03 - Spread mayonnaise evenly on one side of each bread slice. Add Dijon mustard if desired.
04 - Place one bread slice mayo-side up on a plate. Layer with romaine lettuce, sliced turkey breast, and one slice of cheese.
05 - Top with a second bread slice, mayo-side down. Spread mayo on the exposed side, then layer with cooked turkey bacon, tomato slices, and avocado if using.
06 - Finish with the third bread slice, mayo-side down. Gently press down to compact layers.
07 - Cut sandwich diagonally into halves or quarters using a sharp knife. Secure with toothpicks if desired and serve immediately.