Cut off the tops of the bell peppers and remove any seeds inside, discard tops and seeds.
In a medium bowl combine the ground beef, diced onion, breadcrumbs, ketchup, egg, Worcestershire sauce, garlic powder, dried parsley, salt and black pepper. Mix until combined then divide mixture between bell peppers. Set aside.
Line the bottom of your slow cooker with the cubed potatoes (make sure it's an even layer), then add the 1/2 cup water and sprinkle with the 1/2 tsp garlic powder and onion powder. Place the stuffed peppers on top of the potatoes and cover with the lid. Cook on HIGH for 3 to 4 hours or LOW for 6 to 7 hours.
The potatoes will be done when they are fork tender. Use tongs to remove the peppers and carefully tip over to allow any fat to drain out and discard. If desired, place the stuffed peppers in a small baking dish and top with ketchup and pop under your broiler for about 2 to 3 minutes.
Meanwhile mash the potatoes (no need to drain the cooking liquid). Add the sour cream and butter and continue to mash until smooth and creamy. Season with salt and pepper to taste. Enjoy!