Place black beans in a colander & rinse. Add corn & rinse again to begin thawing.
Whisk together lime juice, olive oil, salt, garlic, cumin & chili powder in a large serving bowl.
Add black beans & corn to serving bowl. Add tomato or roasted red pepper & onion. Stir gently with a rubber spatula to mix well & coat everything with the dressing.
Can be made a day or so ahead & refrigerated. Serve cold or at room temperature.