Preheat oven to 375° Fahrenheit.
Add 1 cup uncooked long-grain white rice, 1 15-ounce can black beans,1 cup frozen corn kernels, 1 16-ounce jar salsa, 2 cups chicken broth, 2 tablespoons taco seasoning, 1 cup shredded Mexican-blend cheese, and white parts of 3 sliced green onions to casserole dish.
Stir well until all ingredients are fully combined and well-distributed. Cover casserole dish tightly with aluminum foil.
Place covered dish in preheated oven and bake, covered, for 50 minutes.
After 50 minutes, remove dish from oven and uncover. Taste rice to determine readiness. If needed, recover baking dish with foil and continue baking casserole, checking rice every 5 minutes until rice is tender with no crunch remaining.
When rice is tender, discard aluminum foil cover. Sprinkle remaining 1 cup shredded Mexican-blend cheese on top of casserole. Return baking dish to oven to bake casserole, uncovered, 10 minutes or until cheese is melted
Once cheese is melted, remove dish from oven and set aside. Let casserole rest 10 minutes.
After 10 minutes, garnish casserole with green parts of 3 sliced green onions, chopped fresh cilantro, sliced avocado, and/or sour cream. Serve warm.