1. Preheat oven to 350°.
2. In a frying pan melt butter and fry onion until transparent. Transfer to a bowl and add the ground meat and egg.
3. Soak the slices of bread in water, squeeze and add to meat. Add salt, oregano and pepper. Mix well.
4. Sprinkle bread crumbs to cover a sheet of wax paper. Roll the ground meat over the bread crumbs and form a rectangle of 1 inch thick.
5. Beat the mashed potatoes with the parsley and extend over the meat (reheat the mashed potatoes to help spreading).
6. Using the paper, roll the meat like a jelly-roll; place in a baking sheet. Put slices of bacon over roll and brush with butter.
7. Bake for 1 hour and serve with a tomato or mushroom sauce.