The panino con focaccia ripiena is defined by the seal: the filling goes in before the bread bakes, not after. Where an ordinary focaccia sandwich is split and filled once it is cool, the ripiena, the stuffed version, is a Ligurian construction in which a layer of filling is enclosed between two sheets of oiled dough and baked as one piece. The filling and the bread cook together, so the result is not a sandwich assembled from parts but a single sealed thing, the crust crisping while the centre steams the filling into the crumb.
The craft is in the dough, the oil, and what survives a hot oven sealed inside bread. The two layers of focaccia dough are stretched thin, the lower one laid down, the filling spread to the edges, the upper sheet pressed over and crimped so nothing escapes and steam stays trapped to cook the centre. The filling has to be something that wants the heat: a soft cheese like stracchino that goes molten and binds the layers, greens wilted first so they do not weep raw water into the dough, a cured meat that renders rather than dries. Too wet a filling and the base goes soggy and the seal fails; too dry and the point of baking it in is lost. The oil and salt of the focaccia carry through both crusts, so the bread is doing real flavour work rather than only containing. It is eaten warm, when the sealed centre is still soft and the surface still crisp.
The variations are the Ligurian larder baked in: the classic stracchino seal, the onion or greens version, the one with a cured meat folded into the dough. Each is a different filling enclosed in the same oiled crust, and each deserves its own article rather than being crowded in here.