Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the cooked chicken, uncooked rice, cream of chicken soup, diced tomatoes (with juice), chicken broth, frozen mixed vegetables, garlic powder, onion powder, thyme, salt, and pepper. Mix well until all ingredients are evenly combined.
Pour the mixture into a greased 9x13-inch baking dish, spreading it out evenly.
Cover the dish with aluminum foil and bake in the preheated oven for 45 minutes.
After 45 minutes, remove the foil and stir the casserole. Sprinkle the shredded cheddar cheese on top.
Return the dish to the oven and bake uncovered for an additional 15-20 minutes, or until the cheese is melted and bubbly and the rice is tender.
Let the casserole sit for 5 minutes before serving.