The Polish Boy is a sausage sandwich whose defining feature is that the side dish has been moved inside it. A grilled kielbasa or hot link goes in a bun, and then french fries and coleslaw and barbecue sauce are loaded on top of the sausage, in the bun, so a full plate of food becomes a single handheld thing. The sausage is the anchor, but the sandwich is the stack on top of it. That decision to put the fries under the lid rather than alongside is the whole identity, and everything about the build is arranged to keep that stack from collapsing before it reaches the hand.
The craft is in sequence and structure. The kielbasa is grilled so its casing snaps and renders some fat, which is the savory base the rest of the build sits on. The fries go in hot and directly against the sausage, where they soak up rendered fat and sauce and act as a structural raft that holds the upper layers up. The coleslaw goes on next, cold and acidic and crunchy, and it does the real balancing work: it cuts the fat of the sausage and the fries and keeps a heavy, greasy sandwich from reading as one note. The barbecue sauce is laid over the top, sweet and sharp, binding the slaw and fries to the sausage and dripping down through the whole assembly. The bun has to be sturdy and soft at once, soft enough to compress to the load but strong enough to carry sausage, fries, slaw, and sauce without tearing through the bottom. This is a build that demands to be eaten immediately, leaning forward, because the same fries that hold it together start to go soft under the sauce within minutes. It is street and corner-stand food, made fast and meant to be eaten over its own wrapper.
The variants are small and move with the cook. A hot link swapped for the kielbasa pushes the heat up; some builds add hot sauce over the barbecue sauce or a heavier hand of slaw to push back against the fat. The closely related Polish Girl swaps in pulled pork alongside the sausage. It belongs to the broad American hot dog and sausage-in-a-bun family, and those relatives deserve their own articles rather than being crowded in here.