Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish and set it aside.
In a large mixing bowl, combine the chicken, cream of chicken soup, sour cream, 1/2 cup chicken broth, garlic powder, onion powder, thyme, salt, pepper, and mixed vegetables. Stir until everything is evenly coated in the creamy sauce.
Transfer the chicken mixture to the prepared baking dish and spread it into an even layer.
Place the stuffing mix in a separate bowl. Pour in the remaining 1 1/2 cups chicken broth and melted butter. Stir gently until the stuffing is evenly moistened.
Spoon the prepared stuffing over the chicken mixture, spreading it evenly across the top.
Bake uncovered for 30-35 minutes, until the filling is hot and bubbling around the edges and the stuffing is lightly golden.
Remove the casserole from the oven and let it rest for about 5 minutes before serving. This gives the creamy filling a little time to settle.