Definition: What is Cumberland Pie, you may ask, as it looks almost the same as a Cottage Pie. They are, in fact all but the same: meat and mash and perhaps a bit of cheese. The Cumberland Pie, however, has an extra layer of toasted breadcrumbs.
Some like to mix the cheese in with the mashed potato, some mix the cheese with the breadcrumbs. It is all a matter of personal preference; there is no definitive recipe.