Cut potatoes into 1-inch chunks and chicken into 1-inch pieces, setting them aside in separate bowls.
In a medium bowl, combine the softened cream cheese, minced garlic, parmesan, garlic parmesan sauce, milk, and chicken broth, stirring until the cream cheese is fully incorporated and the mixture is smooth.
Add the prepared potatoes and chicken pieces to your slow cooker, then pour the sauce base from Step 1 over them, stirring gently to combine.
Add the cracked black pepper and stir once more to ensure everything is evenly distributed.
Cover and cook on high for 2½ to 3½ hours, or on low for 4½ to 5½ hours, until the chicken is cooked through and potatoes are tender when pierced with a fork.
Once the chicken and potatoes are fully cooked, add the mozzarella cheese directly to the hot slow cooker and stir frequently for 2-3 minutes until it’s completely melted and incorporated into the sauce.
Ladle the creamy garlic parmesan chicken and potatoes into serving bowls, making sure to distribute the sauce evenly.
Top each serving with fresh chopped parsley for a bright, herbaceous finish and to add visual appeal.
