Many years ago we went to restaurant and ordered roast beef, the chap came out with slices of raw beef, popped it in the oven and a few minutes later roast beef appeared. This Sunday we went to a pub and had roast beef. I wondered if they adopted a similar method as the slices were so uniform they must have been cut on a ham slicer, I suppose the joint could have been roasted then sliced and warmed up by the gravy or could you cook a joint by slicing first and cooking quickly. More thin steak than a roast but caterers must have lots of tricks they use to get meals out quickly.
