Preheat the oven to 350°F (175°C). Lightly coat a 9x13-inch baking dish with nonstick cooking spray.
Add the chicken broth and melted butter to a saucepan. Heat over medium-high heat until the mixture comes to a boil.
Remove the saucepan from the heat and add the dry stuffing mix. Stir gently, cover with a lid, and allow it to stand for 5 minutes. Remove the lid and fluff the stuffing with a fork.
In a large mixing bowl, combine the cubed turkey, frozen vegetables, sliced celery, minced garlic, and condensed cream of chicken soup. Stir until evenly combined.
Transfer the turkey mixture to the prepared baking dish and spread it into an even layer.
Spoon the prepared stuffing evenly over the turkey mixture. This creates the comforting, savory topping that makes this Turkey Stuffing Casserole so satisfying.
Bake uncovered for 30–35 minutes, or until the filling is hot and bubbling around the edges and the stuffing is lightly golden.
Remove the casserole from the oven and sprinkle with chopped parsley.
Allow it to rest for about 5 minutes before serving. Spoon warm gravy over individual portions as desired.