Heat the drippings, add the onion and garlic and sauté until the onion is transparent. Remove to mixing bowl and add the ground beef. Add the egg.
Soften the bread in water, press out the excess water and add bread to the meat. Add the salt, oregano and pepper. Mix thoroughly.
Sprinkle a piece of waxed paper with crumbs. Press the meat on the crumbs to make a rectangle about 1/2 inch thick.
Beat the mashed potatoes with the parsley and spread on top of the meat. (If leftover potato is used, reheat before spreading).
Using the waxed paper as an aid, roll the meat and potatoes, jelly-roll fashion, and place in a loaf pan or on a shallow baking pan. Grease the pan if the meat is very lean. Place the bacon on top if using or brush with additional drippings; baste at least once during baking.
Bake about one hour and serve with a brown sauce made from the pan drippings, or with mushroom, tomato or other sauce.