Set a cast-iron skillet over medium heat. Add the bacon. Cook until browned and as crispy as you like it. Remember, it gets significantly crispier as it cools! While cooking, flip halfway through, and progressively drain the fat into a heatproof glass or bowl. When the bacon is done, transfer to a paper towel-lined plate, and drain the rest of the fat into the glass or bowl.
Now add 2 teaspoons bacon fat back to the skillet. Add the bread and toast until the bottom is browned. Drizzle each piece with another teaspoon bacon fat and flip. Cook until the other side is browned.
Transfer to a plate. Layer the sandwich in this order: bread, lettuce, bacon, tomato (sprinkle with salt and pepper), bread. Slice in half diagonally, from corner to corner, and eat immediately.