Cook rice or quinoa according to package instructions.
In a mixing bowl, combine black beans, thawed corn, cucumber, bell pepper, tomato, red onion, cilantro, olive oil, lime juice, garlic powder, and salt.
In 4 serving bowls, layer a scoop of rice or quinoa, black bean salad, and a dollop of vegan cheese sauce and/or sour cream. Top with a little extra cilantro for garnish, and serve, preferably while rice is still hot.
See above for links to my favorite vegan "cheese" and "sour cream" recipes.