Combine the black beans, corn (no need to defrost), bell pepper, onion, and cilantro in a large bowl.
In a small bowl whisk together the remaining ingredients (except the optional avocado) and pour over the black bean mixture. Toss to thoroughly coat.
Let stand for at least 15 minutes for the corn to fully defrost and flavors to combine–the flavors will continue to improve over time.
When ready to serve, add the avocado**, if using, and toss. Great as a dip with tortilla or corn chips (like Scoops); as a salsa spooned over fish, chicken or steak; mixed into grain-based or green salads, or as a stand-alone salad.