The Portland Voodoo doughnut sandwich is defined by replacing the bread with a fried, glazed, often topping-laden doughnut, which makes the carrier the loudest part of the sandwich rather than the quiet one. Every other sandwich in this catalog chooses bread to support a filling. This one inverts that: a sweet, sticky, decorated doughnut is split and built around a savory center, so the structural and flavor problem is no longer how the bread serves the filling but how a filling survives being put inside a dessert.
The craft is in managing a carrier that fights the build. A glazed yeast doughnut is soft, greasy, and sugar-coated, with none of the structure a roll brings, so the filling has to be something that does not soak it through before it is eaten, which is why the savory center tends toward fried chicken, bacon, or a griddled patty rather than anything wet or sauced. The doughnut is usually split horizontally and the cut faces are sometimes griddled briefly to firm them, because an untreated doughnut collapses under any weight. The whole point is the collision the carrier creates: the glaze's sugar and the fryer oil of the doughnut set directly against salt and fat from the filling, so the bite is sweet and savory at once, with no neutral element anywhere in it. There is no acid or crunch holding it in balance by design; the imbalance is the dish, and it works because it is eaten fast and small, as a novelty rather than a meal.
The variations are a function of which doughnut is used and what goes inside, since the shop's catalog of decorated doughnuts is itself the variable: a plain glazed split around fried chicken reads one way, a topping-heavy doughnut another, and a bacon-and-egg breakfast build runs the same logic in the morning. Each is a single swap on the same inverted frame and belongs in its own article rather than being crowded in here, which is what the rest of the regional catalog is for.