In a small bowl make the dressing by combining the red wine vinegar, olive oil, cumin, coriander, lime juice, salt, and ground black pepper.
Put the black beans in a large bowl. Add the tomatoes, red onion, cilantro, corn, and serrano pepper, if using. Add the dressing and toss. Add avocados, if using, and toss gently.
Chill salad for about 30 minutes or overnight to marinate. Mix one more time before serving.
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