The panino con parmigiana takes a baked casserole and asks it to behave between bread. Parmigiana in its general reading is the layered oven dish of fried vegetable, tomato sauce, cheese, and basil, baked until it sets into a soft, wet slab that is cut with a spoon on a plate. Lifting a portion of that slab into a roll is the whole problem the sandwich exists to solve: a finished bake is moist, structurally loose, and held together only by melted cheese, and the panino has to carry it without the bread dissolving before the last bite. This is the wet-slab build, and what defines it is not the filling so much as the engineering that lets a casserole travel in one hand.
The craft is reducing the water and choosing a loaf that fights it. The parmigiana is best taken from a bake that has rested and firmed rather than served molten and running, cut into a portion thick enough to hold and drained of the loosest sauce at the edge. The bread is a sturdy crusted roll, frequently warmed or lightly toasted so a firm cut face meets the wet filling and slows the bleed. Served slightly warm rather than oven-hot, the cheese is set enough to bind the layers instead of sliding out of the seam. The portion is controlled on purpose: an overfilled panino con parmigiana fails along the bottom crust within minutes, and the entire skill is a measured spoonful held by a bread chosen to take it.
The named directions are the regional vegetables the dish is built on. The aubergine version is the one most people mean and is treated on its own as the Panino con Parmigiana di Melanzane; there are courgette and artichoke bakes that follow the same layered logic, and a few that lean harder on the tomato than the cheese. Each is a distinct bake with its own balance of vegetable, sauce, and melt, and each deserves its own article rather than being crowded in here.