Preheat the oven to 400°F. Arrange the bacon slices in single layer on a foil–lined rimmed baking sheet. Bake until bacon is deeply browned and crispy, 20 to 25 minutes, rotating sheet halfway through baking. Transfer bacon to paper towel–lined plate to drain; discard bacon fat and foil. Adjust the oven temperature to broil.
Meanwhile, core tomatoes and cut into 8 (¼-inch-thick) slices. Place the slices on a sheet of foil and sprinkle lightly with salt and pepper.
Arrange bread slices on the same baking sheet. Broil until lightly browned on 1 side only, 1 to 2 minutes.
Transfer bread, toasted side down, to cutting board. Spread mayonnaise evenly on untoasted sides of bread. Break bacon slices in half. Shingle 4 bacon halves on each of 4 bread slices, followed by shredded lettuce, 4 tomato slices, 2 more lettuce leaves, and 4 more bacon slice halves. Top each sandwich with remaining bread slices, mayonnaise side down. Cut sandwiches in half, corner to corner, and serve.