Read as a salad sandwich, avocado and bacon is a vegetable build that has borrowed a small amount of cured meat to supply what the vegetable cannot. The avocado is the body of the sandwich, soft and rich and mild, and the bacon is there in a thin, crisp quantity to do one job: deliver salt and a hard texture into an otherwise yielding, under-seasoned filling. This is the defining logic of the salad-led version. The bacon is a seasoning and a structural counter, not the centre, and the proportion tips toward the avocado rather than away from it.
The craft is the balance between two textures that would otherwise both be soft. Avocado on bread is one note, and the entire reason the bacon earns its place is contrast: it has to stay genuinely crisp, which means it goes in dry and is laid on at the last moment, because a rasher that softens in contact with avocado loses the snap that justified adding it and the sandwich collapses back into a uniform paste. The avocado is sliced or lightly crushed and seasoned with salt and an acid in its own right rather than relying on the bacon to carry the whole load, since a few rashers cannot salt a sandwich evenly on their own. The bread is given some structure, often toasted, so it does not go down under a wet, rich filling, and salad leaves or tomato can join as the cool, watery side that keeps a fatty centre honest. It is a brunch and lunch-counter sandwich, assembled close to eating because the avocado will not wait.
The variations move the dial along the same axis. More leaves and tomato push it further into salad territory; a richer crumb of avocado pulls it back toward the vegetable; the bacon-led reading, where the rasher is the point and the avocado replaces the sauce, is a different sandwich and deserves its own article rather than being crowded in here.