Line a rimmed baking sheet with parchment paper and spread the bacon evenly on top. Bake until crispy, about 20 minutes. Transfer the bacon to paper towels to drain the oil.
Mix the mayonnaise with the chopped chipotle peppers in a bowl (see Cook's Note). Spread the chipotle mayo on each slice of toast. Arrange the lettuce on four of the toast slices and top with tomato. Sprinkle with salt and pepper. Top with bacon. Place the remaining toast slices on top of the bacon. Cut the sandwiches in half on the diagonal and serve immediately.
For a smoother mix, use a food processor to make the chipotle mayo.
Chipotle mayo can be made 3 days ahead and refrigerated, covered.