Sauté the onion in the oil until translucent. Add the ground chuck, crumble and cook until no longer pink. Drain fat.
Add ketchup and next 7 ingredients. Combine well and simmer for a minute or two. Taste and correct seasoning. Preheat oven to 350°.
Grease a 9" X 13" casserole dish. Add all of the beef mixture. Spoon the mashed potatoes all over the top. Using the back of a spoon, spread the potatoes so they cover the dish entirely. Don't smooth too much. Peaks and valleys are the goal. Sprinkle with a few more parsley flakes.
Bake 30 minutes or until the filling is hot and the potatoes are browning.