Preheat oven to 350 degrees F. Lightly grease a 9x13-inch ovenproof baking dish with nonstick cooking spray.

In a large mixing bowl, combine shredded chicken, uncooked instant rice, cream of chicken soup, sour cream, frozen onion and pepper blend, undrained diced tomatoes with chilies, chicken broth, fajita seasoning, and half of the shredded cheese. Stir until fully and evenly combined. The mixture will look loose and soupy, which is normal.

Pour the mixture into the prepared baking dish and spread evenly with a spatula, smoothing all the way to the edges.

Cover the dish tightly with aluminum foil and bake for 35 minutes.

Remove foil and sprinkle the remaining cheese evenly over the top. Return to the oven uncovered for 10 more minutes, until cheese is fully melted and bubbling at the edges. Tent loosely with foil if cheese browns too quickly.

Let the casserole rest for 5 minutes before serving. Check that internal temperature has reached 165 degrees F.