The piadina con squacquerone e rucola is the build that makes the case for the thin coastal round, because every part of it is calibrated against the bland warm bread it sits in. Squacquerone is a Romagnola fresh cow's-milk cheese so soft it spreads like thick cream and so mild it reads as little more than tang and milk. Rucola, wild rocket, is sharp and peppery and bitter. The warm piadina is faintly savoury and almost neutral. The defining fact is that none of the three works alone in bread: the cheese is a smear without structure, the rocket is a handful of leaves, and the round is plain. Folded together they become a single thing, the soft cheese binding the leaves to the crumb while the bread gives the loose, wet pair something to hold onto.
The craft is the temperature of the assembly and the restraint of the portion. The piadina is cooked thin and folded hot, straight off the testo, because the heat is what slackens the squacquerone from cool and slack to warm and spreadable, sinking it into the blistered surface rather than letting it sit on top. The cheese is kept cold until the last second so it spreads cleanly and so its tang stays bright against the warm dough, and it is applied like a soft dressing because it has no body to slice. The rocket goes in raw and dry and is kept to a handful, enough that its pepper and bitterness register against the milk without turning the fold into a salad. A good build is closed and eaten at once while the contrast is sharpest; a sloppy one overloads the cheese so it weeps through the round, or piles the leaves so the bread cannot close.
The variations are the close Romagnola cousins that swap one element while keeping the soft-cheese logic. There is the version with prosciutto crudo added so the salt and the cured fat answer the tang, the one that drops the rocket for a cleaner two-part build, and the relative that carries the same squacquerone into fried gnocco rather than a griddled round. Each of those is the same cheese-as-bind idea with one decision changed, and each deserves its own article rather than being crowded in here.