Heat a medium nonstick skillet over medium heat. Add the bacon and cook for 5 to 6 minutes, turning halfway until crisp. Transfer to a paper towel to drain excess fat. Leave a little fat in the skillet.

Crack the egg into the skillet and cook until the yolk is set, about 2-3 minutes.

While the bacon and egg are cooking, toast the bread slices. Spread the mayo on the bottom slice.

Assemble the sandwich by placing the lettuce and tomato slices on the mayo-spread bread, then add the cooked bacon and egg on top. Cover with the other slice of toast and cut in half.