Set your oven to 350°F (175°C).
This ensures even cooking throughout the casserole.
Grease your baking dish with cooking spray.
Mix chicken, soup, and sour cream together.
Add diced onion and vegetables if using.
Season with salt and pepper generously.
Stir until everything combines well together.
Combine stuffing mix with melted butter.
Add chicken broth slowly while stirring continuously.
The mixture should be moist but crumbly.
Spread chicken mixture in the greased dish.
Top with the prepared stuffing mixture evenly.
Press down gently with a spoon.
Cover with foil and bake 30 minutes.
Remove foil and bake 15 minutes more.
The top should turn golden and crispy.
Let casserole rest for 5 minutes before serving.
This helps everything set properly together.
Garnish with fresh parsley if desired.