The spinach fold is the quiet, vegetable-led member of the family, and it leans on the piadina for fat and body rather than contrast. Spinach wilted with a little garlic and oil is mild, soft, and faintly mineral; on its own it would slide around with nothing to anchor it. The warm Romagnolo round gives it both a structure and a richness it does not have alone, the blistered, slightly fatty crumb soaking up the garlicky oil and turning a loose tangle of greens into something that holds in the hand and tastes of more than leaf. The defining fact is that this build is a balance of plain against plain, where the bread supplies the weight and the spinach supplies the freshness, and a soft cheese is usually the hinge between them.
Making it well is about not drowning the bread and dressing the greens properly. The dough is flour, lard or oil, water, almost no leavening, rolled thin and cooked dry until it freckles dark and stays pliable, pulled before it sets crisp so the fold does not crack. The spinach is wilted fast in a hot pan with garlic, then drained hard, because wet greens are the quickest way to turn the inside of a piadina to paste; the aim is glossy and barely collapsed, not stewed and sodden. Squacquerone, stracchino, or fresh ricotta is smeared on the warm surface to add the fat and tang the greens lack and to glue the loose filling to the crumb. It is folded in half and eaten warm, while the bread is soft and the cheese is still slack.
The near relatives change one element and stay close. There is the version with sausage cooked alongside for a meatier, heavier read, the one that swaps spinach for bitter chard or wild greens, and the fold dressed only with ricotta and a little Parmigiano for the plainest vegetable build. Each is the same warm round meeting a single changed element, and each deserves its own article rather than being crowded in here.