The chicken fillet roll is built to order at a deli counter, and the made-to-order assembly is the whole identity, not the fillet itself. A breaded chicken fillet is cooked hot and crisp behind the counter of an Irish shop, then slid into a buttered baguette or soft roll while the customer calls the rest of the build down the line: which sauce, whether cheese, salad or none, on or off. It is not a fixed recipe handed over finished. It is a frame, a hot crisp fillet in bread, finished differently for every person who orders one, and that act of specifying it at the counter is what the sandwich is.
The craft is timing and the defence of the crumb against everything added to it. The fillet has to go into the roll while its coating is still crisp from the fryer or hot plate, because a breaded fillet left to sit steams its own crust soft, and a soft crust collapses the entire point. Butter on the roll is laid first as a barrier between the bread and whatever wet sauce follows, so the crumb does not go through before the customer leaves the shop. The sauce is the pivotal choice and it is the customer's: taw, garlic, mayonnaise, a peppered or a curried sauce, each one a different sandwich built on the same fillet, applied in a measured stripe rather than a flood so it dresses without drowning the coating. Salad, when taken, is added dry so it does not undo the work the butter is doing. The roll is sized to the fillet so the bread-to-meat ratio holds rather than reading as a baguette with a strip of chicken lost inside it.
The variations are the order itself spoken aloud. Cheese melted against the hot fillet, a spiced sauce in place of a mild one, the breakfast version with rashers added, the spice-bag-adjacent loaded build: each is the same counter assembly answered differently. Each deserves its own article rather than being crowded in here.