Lay your bacon out on a baking sheet lined with aluminum foil in a single layer. Place the baking sheet into a preheated oven for 15 minutes or until cooked to your preference.
While the bacon is cooking, spread a thin layer of mayonnaise on one side of each slice of sourdough toast.
Mash your avocado and season with salt, to taste.
Add slices of swiss cheese to one slice of sourdough bread.
Spread avocado generously over the slice of toast without cheese on it. Spread any extra avocado over the swiss cheese.
Building on top of the slice of sourdough with only avocado on it (and no cheese) for the rest of this recipe, slice your tomato into ¼" slices and lay them onto this half of the sandwich.
When the bacon is done, lay the bacon slices onto a paper towel to drain excess fat then while still warm arrange on top of the tomato slices.
Top the tomato and bacon with whole leaves of red leaf lettuce, with the spine of the lettuce facing up.
Take the sourdough slice with the cheese and match it up with the slice we have been building on top of. Cut your sandwich in half with a bread knife and serve.