Adapted from a recipe in the pre-Christmas issue of the Australian magazine 'New Idea' which contained several recipes which make good use of Christmas day leftovers. This recipe could, of course, be made at any time of year when you have left over roast beef. At other times, you could always buy sliced roast beef at your local deli. You can either halve your bagels and toast the halves, or simply warm them in the oven. Whichever you prefer. :) And if you know you like lots of mayonnaise or dressing on burgers or bagels, consider increasing the quantities of the cheese and the mayonnaise. The other recipes posted from this collection are Recipe #344949, Recipe #345416 and Recipe #345446.