Brown the ground beef in a nonstick skillet. Drain well. Place meat in slow cooker. Add cubed potatoes, chopped onion, and tomato sauce. Stir in salt, pepper, water, and hot pepper sauce if you wish. Cover and cook on high until mixture starts to simmer, about 1 hour. Turn to low and continue cooking until potatoes are tender, about 2 1/2 to 3 hours. Garnish each bowl with chopped parsley if desired.
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