Preheat a skillet or griddle over medium heat.
Lightly butter one side of each slice of bread.
Toast the bread slices in the skillet, buttered side down, until golden brown and crisp, about 2-3 minutes per side. Remove and set aside.
On three of the toasted bread slices, spread 1 teaspoon of mayonnaise evenly on the unbuttered side.
Place 2 slices of cooked turkey breast on each of the three slices with mayonnaise.
Add 2 leaves of romaine lettuce on top of the turkey on each slice.
Place 2 slices of tomato on top of the lettuce for each sandwich layer. Sprinkle a pinch of salt and freshly ground black pepper on the tomato slices.
Add 2 slices of cooked beef bacon on top of the tomato layer on two of the bread slices.
Stack the slices to form the sandwich: place one slice with turkey, lettuce, and tomato on top of another slice with turkey, lettuce, tomato, and bacon.
Top each sandwich stack with the remaining toasted bread slice, buttered side up.
Secure each sandwich with two wooden toothpicks, one near each end.
Cut each sandwich diagonally into four triangular quarters.
Serve immediately with your choice of side.