Layer the potatoes and 1 tablespoon of the minced onion in a buttered 8x12 inch or 2 quart baking dish.
Sprinkle with half the salt, half the pepper and the parsley flakes.
Combine the ground beef, evaporated milk, rolled oats, chili sauce, the remaining 4 tablespoons minced onion, 1 teaspoon salt and 1/4 teaspoon pepper in a large bowl; mix well.
Spread the ground beef mixture evenly over the potatoes.
Decorate the top with a little ketchup.
Bake, uncovered, at 350 degrees for 1 hour.