Combine potatoes, olive oil, 3/4 teaspoons salt, 1/2 teaspoon black pepper, and paprika in the bottom of a slow cooker and stir until well coated. Add chicken pieces on top and sprinkle with remaining salt and pepper. Whisk Parmesan garlic sauce and water together in a bowl until well incorporated. Pour mixture over chicken and potatoes.

Cook on High for 4 hours (or on Low for 6 hours), or until chicken is cooked through and potatoes are tender. During the last 20 minutes of cooking, add mozzarella and Parmesan and continue to cook, covered. Sprinkle with parsley to serve.