Use a can opener to open the can of black beans, then drain and rinse them thoroughly under cold water. Set aside to drain completely.
Measure out one cup of corn kernels—use fresh, frozen, or canned—and add them to a large mixing bowl.
Dice the red bell pepper into small pieces, then add to the bowl along with the drained beans.
Finely chop half a red onion and mix it into the bowl with the other ingredients.
In a small jar or dressing shaker, combine lime juice, olive oil, ground cumin, and a pinch of salt and pepper. Shake vigorously until well blended and slightly emulsified.
Pour the dressing over the salad ingredients in the bowl and gently toss everything together until evenly coated.
Cover the bowl and refrigerate for at least 15 minutes to allow flavors to meld and the salad to chill.
Give the salad a gentle toss again, taste, and adjust seasoning with extra salt, pepper, or lime juice if needed.
Serve the salad chilled in bowls or on a platter, garnished with fresh herbs or avocado if desired, and enjoy this refreshing, flavorful dish.