The panino con Käsespätzle is a Tyrolean sandwich whose filling is a cheese-and-pasta dish forced between bread. Käsespätzle is the Alpine comfort plate of the region: small irregular egg-dough dumplings, the Spätzle, layered with a strong mountain cheese until they pull into strands, usually crowned with fried onion. Spooned hot into a roll, it puts cooked starch inside raw starch, carb on carb, which is exactly as heavy as it sounds and entirely the point. This is the unusual one, a full skillet of cheese-bound noodles treated as a sandwich filling rather than a plated meal, and the build follows from that decision.
The craft is making a loose, molten dish behave inside bread. The Spätzle are bound with enough melted cheese to hold together as a mass rather than scatter, and the portion is controlled and pressed slightly into the crumb, because an overfilled roll of cheesy noodles fails on the first bite and slides apart in the hand. It goes in hot, straight from the pan, while the cheese still pulls and before it sets into rubber on cooling. The roll is plain and sturdy, sometimes warmed or lightly toasted so it firms against the moisture and the fat instead of going to paste. The fried onion is worked through for its sharpness and crunch, the one counter-texture in an otherwise soft and rich thing, and nothing else is added because the dish is already complete on the plate.
The variations are essentially what the Spätzle are dressed with before they go in. There is the plain cheese build, the one heavy with fried onion, and the version finished with a little of the browned butter the noodles were tossed in. The plate version, the same Käsespätzle served in a dish with no bread at all, is a different thing entirely. The wider Germanic-north repertoire of this corner, the canederli, the Gröstl, the speck on rye, follows its own logic, and each of those deserves its own article rather than being crowded in here.