Toast the bread in the same skillet with the bacon fat over medium-low heat until golden brown. Flip and brown the second side.
Move the bread to a cutting board and spread the mayonnaise on both pieces. Stack the lettuce on one piece of bread and then top with the tomato slices before sprinkling generously with coarse salt and freshly cracked pepper. Layer the bacon onto the sandwich, breaking the pieces in half if they don't fit. Top with the remaining slice of bread and cut in half diagonally.