In a medium saucepan, combine the shredded chicken and buffalo sauce over medium heat. Stir until the chicken is heated through and well coated with the sauce, about 5 minutes.
While the chicken is heating, prepare the brown rice according to package instructions if not already cooked.
In serving bowls, layer the cooked brown rice as the base.
Top the rice with the buffalo chicken mixture, followed by black beans, corn, cherry tomatoes, avocado, and shredded cheddar cheese.
Drizzle ranch dressing over the top and sprinkle with sliced green onions.
Serve immediately while warm, or chill for 30 minutes for a refreshing cold option.