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 crispy, about 2-3 minutes per side. Remove and set aside.
In the same skillet, cook the turkey bacon slices until crispy, about 3-4 minutes per side. Remove and drain on paper towels.
Spread about 1 tablespoon of mayonnaise on the unbuttered side of three toasted bread slices.
On one bread slice with mayonnaise, layer 2 slices of turkey breast, 2 leaves of romaine lettuce, and 2 slices of tomato. Season the tomato lightly with salt and pepper.
Place a second slice of toasted bread, mayonnaise side down, on top of the tomato layer.
On this second bread slice, spread mayonnaise on the top side and layer 2 slices of turkey bacon, 2 slices of turkey breast, and 2 leaves of romaine lettuce.
Top with the third slice of toasted bread, mayonnaise side down, to complete the sandwich.
Using a sharp knife, carefully cut the sandwich diagonally into quarters, securing each quarter with a toothpick if desired.
Serve immediately with your choice of side.