Preheat the oven to 375°F.
Drain and briefly rinse the black beans. Add the dry rice, black beans, corn, salsa, chicken broth, chili powder, and oregano to an 8” x 8” square casserole dish. Stir until everything is evenly combined.
Cut the chicken breasts into three pieces each. In the casserole dish, push the chicken pieces down into the rice-salsa mixture. Try to push them down as far into the liquid as they’ll go. Cover the casserole dish tightly with foil. Bake for one hour.
Take the casserole dish out of the oven, and test the rice with a fork to make sure it is tender. If it is not, recover the dish, return it to the oven, and bake for another 10–15 minutes. When the rice is tender, sprinkle the cheese over top, and return the casserole to the oven for a few minutes, or until the cheese has melted. Add the sliced green onions on top after baking, and serve hot.