Warm the olive oil in a large skillet set over medium-high heat. Add the beef pieces, seasoning them with salt, pepper, and smoked paprika. Sear until browned on all sides without cooking through fully. Take off the heat and set aside.
In a mixing bowl, blend together the condensed mushroom soup, sour cream, beef broth, Worcestershire sauce, garlic powder, and onion powder until you have a uniform mixture.
Coat the inside of your slow cooker lightly with nonstick spray. Begin assembling the casserole by placing half of the potato slices in an even layer at the base. Follow with half the sliced onions, then half of the seared beef, and a portion of the shredded cheddar.
Drizzle half of the prepared creamy mixture evenly over the layered ingredients. Repeat this layering process using the remaining potatoes, onions, beef, cheese, and the rest of the sauce.
Secure the lid on the slow cooker and cook on LOW for approximately 6 hours, or on HIGH for 3 to 4 hours, until the potatoes are fork-tender and the beef is cooked through.
About 10 minutes before serving, sprinkle the remaining cheddar cheese over the top of the casserole. Cover again and allow the cheese to melt thoroughly.
Once ready, finish the dish with a garnish of freshly chopped parsley and serve immediately alongside your favorite side salad or a serving of steamed vegetables.