Drain the canned black beans and rinse them thoroughly under cold water, then let them sit to dry slightly.
Finely chop the red onion and cilantro, then soak the onion in cold water for 10 minutes to mellow its sharpness.
In a large mixing bowl, combine the rinsed beans, drained onion, and chopped cilantro.
Using a citrus juicer or hand-held squeezer, extract the juice from the lemon and pour it over the bean mixture.
Add the olive oil to the bowl, then toss everything together until evenly coated and vibrant.
Season the salad with salt and pepper to taste, then give it one last gentle toss to distribute the seasoning evenly.
Let the salad sit at room temperature for about 10 minutes to allow flavors to meld, or refrigerate for up to 2 days, bringing it back to room temp before serving.
Serve the black bean salad in bowls, garnished with extra herbs if desired, and enjoy its fresh, zingy flavor.