Prepare the oven and dish: Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with butter or nonstick spray to prevent sticking and ensure easy serving later.

Prepare the stuffing: In a medium bowl, combine the stuffing mix with the chicken broth and melted butter. Stir gently until the stuffing is evenly moistened. Let it sit for about 5 minutes so it can absorb the liquid and soften slightly.

Mix the creamy base: In a large mixing bowl, combine the cream of chicken soup, sour cream, milk, garlic powder, onion powder, black pepper, and salt. Stir well until the mixture becomes smooth and well blended.

Assemble the casserole: Add the cooked chicken and frozen vegetables into the creamy mixture. Stir until everything is evenly coated. Then, spread this chicken mixture evenly into the prepared baking dish.

Add the stuffing layer: Spoon the prepared stuffing evenly over the top of the chicken mixture, gently spreading it out to cover the surface. Try not to press it down too firmly so it stays light and fluffy during baking.

Add cheese (optional): If using cheddar cheese, sprinkle it evenly over the stuffing layer for extra flavor and a golden finish.

Bake the casserole: Place the dish in the preheated oven and bake uncovered for 35–40 minutes, or until the casserole is hot throughout and the top is golden brown. The edges should be slightly bubbly.

Finish and serve: Remove from the oven and let the casserole rest for about 5–10 minutes before serving. This helps it set and makes it easier to slice. Garnish with fresh parsley if desired and serve warm.