2. Prepare the Roast Beef. You can use roast beef shredded mixed with gravy or for a quick and easy meal I like to use Lou’s Beef Pot Roast. Make as per package directions either on stove top or in the oven if you have the time but I just use the microwave because the beef is already cooked and you are just really heating it up. I add both packages to a large bowl, cover with a microwave safe splash guard or lid and microwave for 6 minutes or until heated through.