Heat olive oil in a large skillet over medium high heat. Sauté peppers until slightly softened, about for 5 minutes. Add mushrooms, and sauté 2 minutes more. Add rice, beans, coriander, garlic powder, and chili powder; sauté 1 more minute. Stir in 2 cups water, and bring to a boil. Reduce heat to low and cover pot. Simmer until all the liquid is absorbed and the rice is tender, about 20 to 23 minutes. Remove from heat, and stir in cheese, olives, scallions, and green chilies, if desired, and serve.