Cook the bacon in a large frying pan for 5-7 minutes, turning once, until crisp on both sides, then drain on kitchen paper.
Toast the bread on both sides, then spread on side of each slice with 1 tablespoon of mayonnaise.
Put two lettuce leaves on each of two slices of toast and sprinkle with salt and pepper.
Put one slice of turkey on top of the lettuce on each sandwich base, then top with another slice of toast, with the mayonnaise side facing up. Put the rest of the lettuce leaves on top and add the tomato slices then the crispy bacon.
Cover with the other two slices of toast, mayonnaise side facing down. Leave the sandwiches whole, or cut into four triangles, and pierce with long toothpicks for the American diner look.