Preheat a skillet or grill pan over medium heat.
Spread 1 teaspoon of softened butter evenly on one side of each slice of French bread.
Place the bread slices buttered side down on the skillet and toast until golden brown and crispy, about 2-3 minutes per side. Remove from heat.
Spread 1 tablespoon of mayonnaise on the non-toasted side of 4 slices of the toasted French bread.
On two of the mayonnaise-coated slices, layer 4 leaves of romaine lettuce, 4 slices of tomato, and season lightly with salt and freshly ground black pepper.
Add 4 slices of cooked turkey breast on top of the tomato layer.
Place one slice of cheddar cheese over the turkey, then add 2 slices of cooked beef bacon.
Top each sandwich with the remaining mayonnaise-coated bread slices, mayonnaise side down, to close the sandwich.
Using a sharp knife, carefully cut each sandwich diagonally into two triangles.
Secure each sandwich half with toothpicks if desired and serve immediately.