To a medium mixing bowl, add the can of soup, sour cream, and French onion soup mix. Stir until well combined. Set aside.
Lightly coat the crock pot with non-stick cooking spray. Add the hashbrowns, kielbasa, onion, and 2 cups of cheddar cheese to the crock and mix.
Pour the soup mixture over top of the potatoes and sausage and stir until well mixed.
Cover and cook on LOW for 4.5 hours (or until the potatoes are tender and cooked through). Uncover and top with the remaining 1 cup of cheese. Cover and cook until the cheese is melted, about 10-15 minutes.
Serve warm, sprinkled with chopped parsley for garnish, if desired.