01 - Preheat a skillet over medium heat and cook turkey bacon until crisp, about 3 to 4 minutes per side. Drain on paper towels.
02 - Lightly butter one side of each bread slice and toast in a skillet or toaster until golden brown.
03 - Spread mayonnaise and Dijon mustard, if using, evenly on one side of each toasted bread slice.
04 - On one bread slice (mayo side up), layer romaine lettuce, half the turkey slices, tomato, red onion, and half of the turkey bacon. Top with a second bread slice (mayo side up) and repeat the layers with the remaining ingredients. Finish with the last bread slice, mayo side down.
05 - Secure each sandwich with toothpicks and slice into halves or quarters as desired.