Preheat oven to 400 °F (200 °C)
In a 9×13-inch baking dish, combine diced onion, red bell pepper, uncooked rice, fajita seasoning and cayenne (if using)
In a bowl or measuring cup, whisk chicken broth with green chiles, tomato paste and olive oil
Pour the broth mixture into the baking dish and stir to blend with vegetables and rice
Add shredded chicken, black beans and corn to the casserole and mix until well combined
Cover casserole with aluminum foil and bake until most liquid is absorbed and rice is tender
Remove foil and sprinkle shredded cheese evenly over the top
Return to oven until cheese melts and turns slightly golden
Let cool slightly before serving with optional toppings