Preheat your oven to 350°F (175°C) and lightly grease a 9×13 inch baking dish with a bit of the olive oil.
In a large skillet over medium heat, brown the ground beef with the chopped onion until the beef is no longer pink and the onions are soft. Drain any excess fat.
Season the beef mixture with salt, pepper, garlic powder, and papaprika, then spread half of the mixture evenly over the bottom of the prepared baking dish.
Layer half of the potato slices over the beef, then sprinkle with one cup of cheddar cheese. Repeat layers with the remaining beef and potatoes.
In a small bowl, whisk together the condensed soup and milk until well combined. Pour this mixture over the potato layers, ensuring it seeps down into the casserole.
Cover the baking dish with aluminum foil and bake for 1 hour.
Remove the foil, sprinkle the remaining cheese over the top, and bake, uncovered, for an additional 20-30 minutes or until the cheese is bubbly and the potatoes are tender.
Let the casserole stand for 10 minutes before serving. Garnish with fresh parsley for a pop of color.