In a medium saucepan, combine the shredded chicken and buffalo sauce over medium heat. Stir until the chicken is heated through and well-coated in 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, and diced avocado.
Sprinkle shredded cheddar cheese and chopped green onions on top.
Drizzle ranch dressing over the bowls if desired. Serve immediately.