In a large bowl, stir together the beans, tomatoes, corn, onion, pepper, and Napa cabbage. Dress with half the dressing, then taste to see if you want more. I like it with a half cup of dressing.
Divide the rice into 4 bowls. Top with the dressed vegetable mixture, then add avocado and any of the additional optional toppings. Serve immediately.
Note: You can prepare the rice, as well as the bean/vegetable mixture, ahead of time. Refrigerate until you’re ready to serve it, then warm the ingredients briefly on the stove. Add the dressing and avocado just before serving.