Cut the chicken breasts into 1-inch chunks and place them in your slow cooker. Dice the white onion into small pieces. Having your chicken prepped and ready ensures even cooking throughout the slow cooker.

In a bowl, whisk together the cream of chicken soup and sour cream until smooth and well combined. This creates a rich, creamy base that will coat the chicken evenly. I like to whisk these together separately before adding to the slow cooker rather than stirring them in—it ensures there are no lumps and creates a silkier sauce.

Pour the creamy sauce mixture from Step 2 over the chicken in the slow cooker and stir to coat. Add the diced onion from Step 1 along with the parsley, garlic powder, and black pepper. Stir everything together gently so the chicken is well distributed and the seasonings are evenly incorporated throughout the sauce.

While the chicken cooks, combine the stuffing and melted butter in a bowl, tossing gently until the stuffing is evenly moistened—don't overmix or it will become mushy. For the timing, I add this topping during the last 45 minutes of cooking (whether you're cooking on low or high) so it stays light and doesn't become soggy. Spread the stuffing mixture evenly over the top of the chicken and sauce.

Cover the slow cooker and cook on low for 6 to 7 hours, or on high for 3 to 4 hours. The chicken should be tender and cooked through. If you prefer crispier stuffing (optional), uncover the slow cooker for the final 45 minutes of cooking—this will reduce some moisture and allow the top to brown slightly.

Once cooking is complete, taste the dish and adjust seasoning with additional salt and pepper as needed. The sauce will have developed rich flavors from the long, slow cooking. Spoon the creamy chicken and stuffing into serving bowls, making sure each portion gets some of the sauce and a generous amount of the stuffing topping. Garnish with fresh parsley if desired.