Preheat your oven to 400°F and grease a 9x13-inch baking dish lightly with nonstick spray.
In a medium bowl, combine the stuffing mix with hot water. Stir and let sit for 5 minutes to soften.
In the greased baking dish, mix together the diced chicken, sour cream, cream of chicken soup, and thawed vegetables until evenly combined.
Spread the softened stuffing mixture evenly over the top of the chicken mixture.
Bake uncovered for 25–30 minutes, or until the casserole is bubbly and the stuffing is golden brown on top.
Let it rest for 5 minutes before serving. Enjoy!