This odd dish appears in the Fanny Farmer cookbook. The salty olives and sweet raisins make a delicious contrast. We've modified the recipe to be a little lighter and suit our tastes. It's also fine with white rice, and can be made with ground beef or ground pork, or leftover cooked meat. The googling I've done seems to imply that this is the Spanish version of hash, and it is indeed a good way to use up leftover pot roast and/or rice. You can also cook the rice while cooking the other ingredients; just start cooking the meat about 10 minutes before the rice is done.