Place the chicken breasts in a single layer at the bottom of a 6-quart slow cooker. Keeping them in one layer helps them cook evenly and absorb all the flavors. Fresh chicken works best for the most reliable cooking results.
Pour the cream of chicken soup over the chicken breasts. Add the sour cream and gently swirl the two ingredients together using a spatula. This creamy layer keeps the chicken moist throughout the cooking process.
Sprinkle the diced white onion and dried parsley evenly over the creamy layer. These ingredients add a subtle savory flavor that complements both the chicken and stuffing. Distribute them evenly for the best taste in every bite.
In a small bowl, combine the dry stuffing mix with the melted butter. Toss everything together until the breadcrumbs are lightly coated. The butter helps the stuffing stay flavorful and develop a better texture during cooking.
Sprinkle the buttered stuffing mixture evenly over the top of the chicken mixture. Try to cover the surface as evenly as possible. This creates a delicious topping that absorbs the creamy sauce underneath.
Cover the slow cooker with the lid and cook on LOW for 6–7 hours or HIGH for 3–4 hours. During this time, the chicken becomes fork-tender while the stuffing absorbs all the savory flavors. Avoid opening the lid too often, as it releases heat.
If you prefer a firmer stuffing texture, remove the lid during the last 45 minutes of cooking. This helps some of the moisture evaporate. The stuffing will not become crispy, but it will be slightly more structured.
Once cooked, garnish with fresh parsley if desired. Serve immediately while warm for the best texture and flavor. Pair it with your favorite side dishes for a complete meal.