Drain and rinse the canned black beans thoroughly under cold water until the liquid runs clear, then transfer them to a large mixing bowl.
Chop the cherry tomatoes in half or dice them into small pieces, then add to the bowl with the beans.
Finely chop the red onion and fresh cilantro, then sprinkle both over the bean mixture for a burst of flavor and color.
Crumble the feta cheese over the salad, distributing it evenly for creamy saltiness in every bite.
In a small jar or bowl, whisk together lime juice, olive oil, toasted cumin (if using), salt, and pepper to make a bright, zesty dressing.
Pour the dressing over the salad ingredients, then gently fold everything together with a spoon or spatula until the beans and vegetables are coated evenly.
Let the salad sit at room temperature for about 15 minutes to allow the flavors to meld and the herbs to release their aroma.
Give the salad one last gentle toss, taste, and adjust the seasoning with more lime, salt, or pepper if needed before serving.