The panino con coppiette is a sandwich made from a snack meant to be eaten on its own. Coppiette are thin strips of pork, once horse, salted and worked hard with chilli, fennel, and pepper, then air-dried until they are chewy, leathery, and intensely seasoned, the Lazio version of a cured meat stick sold by the norcineria and the country osteria to be gnawed alongside a glass of wine. Putting them in bread is a way of softening that intensity into something a meal can carry. The sandwich is defined by the chew and the heat of the strips, and the bread is there to give them room and absorb their pepper.
The craft is in handling a meat this dry and this loud. Coppiette are tough by design, so they are sliced thin and often across the strip, or warmed slightly so they slacken enough to bite cleanly without dragging the whole filling out in one pull. The chilli and fennel are forceful, which means the bread is a plain, soft-crumbed roll chosen to take the spice and the dryness, sometimes brushed with a little oil so the leathery meat has something to read against and the crumb does not feel parched beside it. There is no need for a sharp condiment: the cure already carries its own heat and acid edge, and the discipline is to let the strips be the whole statement rather than to mute them under something else.
The variations are about taming the chew and the fire, each its own preparation rather than a list here. There is the version laid against a soft fresh cheese that cools the chilli, and the one with a few oil-dressed greens to break the dryness; both are the same dried strip met by a softening counterpart. The wider Lazio norcineria tradition, the cured pork snacks and dried meats of the Roman countryside among it, follows the same logic of one intense cured thing given a plain bread, and each deserves its own article rather than being crowded in here.