2) Place the bread slices on a sheet pan and toast them for 5 minutes. Turn the slices and toast for 1 more minute, until all the bread is evenly browned on both sides.
3) Place 2 slices of the bread on a cutting board. Spread each slice with about 1 tbsp of mayonnaise and cover with a layer of lettuce leaves.
4) Peel the avocado and slice it 1.5-cm thick. Toss the avocado slices gently with the lemon juice, and arrange on top of the lettuce leaves. Place 3 slices of bacon on top of each sandwich and then add a layer of tomato slices on top of the bacon. Sprinkle liberally with salt and pepper.
5) Spread each of the remaining 2 slices of toasted bread with 1 tbsp of mayonnaise and place, mayonnaise side down, on the sandwiches. Cut in half and serve.