Preheat oven to 400° F. Line a rimmed baking sheet with foil.
Arrange the bacon in single layer on the foil–lined baking sheet. Bake until bacon is deeply browned and crispy, 20-25 minutes, rotating sheet halfway through baking. Transfer bacon to paper towel–lined plate. Once cool enough to handle, break each slice of bacon in half.
Meanwhile, in a small bowl, whisk together the mayonnaise, basil and lemon zest. Set aside.
Place tomato slices on a paper towel and sprinkle with salt and pepper.
Toast the bread in a toaster oven or under the broiler until golden brown.
Spread the basil mayonnaise on one side of each slice of toasted bread. Top four of the slices of bread with lettuce, tomato, and bacon. Top each sandwich with remaining bread slices.
Cut sandwiches in half diagonally and serve.