Preheat the oven to 350°F (175°C).
In a large mixing bowl, combine the shredded turkey, frozen mixed vegetables, cooked rice, cream of mushroom soup, milk, half of the shredded cheese, garlic powder, onion powder, salt, and pepper. Mix until well combined.
Pour the turkey mixture into a greased 9x13-inch baking dish, spreading it evenly.
In a separate bowl, combine the breadcrumbs with the melted butter and the remaining shredded cheese. Mix until the breadcrumbs are evenly coated.
Sprinkle the breadcrumb mixture over the turkey casserole.
Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes.
After 30 minutes, remove the foil and bake for an additional 15 minutes, or until the top is golden and crispy.
Remove from the oven and let it sit for a few minutes before serving.