Drain and rinse the canned black beans thoroughly under cold water to remove excess salt, then transfer them to a large mixing bowl.
Add the finely chopped red onion and diced bell pepper to the beans, giving the mixture a gentle toss to combine the colorful vegetables evenly.
In a small jar or bowl, shake together the fresh lime juice, olive oil, minced garlic, salt, and chili flakes until well combined and slightly emulsified.
Pour the dressing over the bean mixture and toss gently to coat all the ingredients evenly, watching the beans soak up the bright, tangy flavors.
Chop the fresh cilantro finely and fold it into the salad just before serving, allowing its fragrant aroma to stay lively.
Let the salad sit for at least 15 minutes in the fridge to allow the flavors to meld and develop, then give it a quick toss before serving.