Or... grind it up and make hash... use some for brekfast and freeze the rest for later:
4 med. potatoes (raw)
1 med. onion
2-3 stalks celery
1/3 c. beef stock or water
Salt and pepper to taste
Oil for frying
1 1/2 c. ground roast beef (leftovers usually)
Grind beef; set aside. Grind potatoes, onion, and celery; fry in oil. Turn or stir occasionally until potato is half done, adding stock to prevent sticking. Stir in meat and finish cooking, adding salt and pepper to taste. Brown and fold over.
We've also added a couple of finely chopped carrots and some green pepper... depends on taste.
Additionally, if you don't have a meat grinder you can simply cut the roast in small cubes. This makes a great soup base, by the way...