Drain and rinse the black beans under cold water until the water runs clear, then gently pat them dry with a towel.
Finely chop the red onion and cilantro, then set them aside to allow their flavors to start melding.
Add the rinsed beans, chopped onion, and cilantro to a large mixing bowl, then sprinkle with a pinch of salt.
Zest the lemon directly over the bowl, then squeeze out about three tablespoons of fresh lemon juice using a citrus juicer, adding it to the mixture.
Pour in the olive oil, then gently toss everything together with a spoon or tongs until the beans are evenly coated and the herbs are distributed.
Taste the salad and adjust seasoning with more salt or lemon juice if needed, then cover and let sit in the fridge for at least 30 minutes to allow flavors to develop.
Give the salad a gentle toss again before serving, ensuring it looks vibrant and fresh with herbs and onions visible, ready to enjoy.