Preheat oven to 375 degrees. Gease an 8x12-inch baking dish.
In a skillet over medium heat, brown ground beef until crumbly. Drain excess grease, reserving 3 tablespoons pan dripping.
In a large bowl combine cooked ground beef, reserved pan drippings, milk, eggs, thawed potatoes with onions and peppers, flour, salt, and oregano. Mix well.
Press the mixture into a prepared baking dish.
Bake at 375 degrees for 25 minutes, or until set and lightly browned.
Garnish with parsley if desired and serve with spaghetti sauce on the side if using.