Preheat oven to 350°F (175°C) and grease a 9×13 inch baking dish with olive oil.
Brown ground beef and onion in a skillet, then season with salt, pepper, garlic powder, and paprika. Layer half in the baking dish.
Add a layer of potato slices and half the cheese. Repeat with remaining beef, potatoes, and another layer of cheese.
Mix condensed soup and milk; pour over casserole.
Cover with foil and bake for 1 hour. Uncover, add remaining cheese, and bake until bubbly and potatoes are tender.
Let stand for 10 minutes before serving. Garnish with parsley.
