Spray your 3-quart slow cooker with cooking spray.
Place the chicken in the bottom. Season with poultry seasoning, garlic powder and pepper.
Scatter the diced onion over the chicken.
Mix together the cream of chicken soup, sour cream and chicken broth. Pour the mixture over the chicken.
Prepare the stuffing: toss the stuffing mix with ½ cup water or chicken broth and the melted butter. Just moisten it—don't make it soggy.
Spread the stuffing evenly over the top. Cover and cook: LOW: 4–5 hours HIGH: 2½–3 hours
Let it rest uncovered for about 10 minutes before serving.