In a large mixing bowl, combine ground beef, bread crumbs, Parmesan cheese, diced onion, egg, Worcestershire sauce, thyme, salt and pepper. Form the mixture into a round loaf, small enough to fit into your pressure cooker.
Warm the cooker, with the lid off. Heat oil on HIGH or “brown” until sizzling.
Place onion 1/4 cup minced onion in the cooker and sauté until translucent, 4-5 minutes.
Stir in ketchup and beef stock and top with rounded meatloaf. Securely lock the pressure cooker's lid and set for 15 minutes on HIGH.
Let the cooker's pressure release naturally for 10 minutes before quick releasing any remaining pressure. Serve topped with sauce from the cooker.