Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the cooked, shredded chicken, uncooked rice, cream of chicken soup, cream of mushroom soup, chicken broth, and milk. Stir well until everything is combined.
Add in the frozen mixed vegetables, garlic powder, onion powder, black pepper, and salt. Mix until all ingredients are evenly distributed.
Transfer the mixture into the greased 9x13-inch baking dish, spreading it evenly.
Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes.
After 30 minutes, remove the foil and stir the casserole gently. Return it to the oven, uncovered, and bake for an additional 10 minutes.
Once done, remove the casserole from the oven and sprinkle the shredded cheddar cheese on top. Place back in the oven for 5 minutes, or until the cheese is melted.
Let the casserole sit for a few minutes before serving.