Combine the potatoes with olive oil, kosher salt, ground black pepper, and paprika in the bottom of your slow cooker. Stir until everything is well coated.
Place the skinless boneless chicken breasts on top of your seasoned potatoes. Sprinkle them with any remaining salt and pepper.
Whisk together your creamy Parmesan garlic sauce with water or chicken stock until fully incorporated. Pour this mixture over both the chicken and potatoes.
Cover your slow cooker and set it to cook on High for about 4 hours or Low for approximately 6 hours.
During the last 20 minutes of cooking time, sprinkle shredded mozzarella cheese over everything and add grated Parmesan if desired.
Once finished cooking, sprinkle chopped fresh parsley on top before serving.