Drain the black beans in a sieve and rinse under cold water. Drain again and drop it in a salad bowl or deep plate. Drain the corn, keep the water and add the corn to the beans.
Wash the red pepper and the tomatoes, take out the seeds and cut them into small cubes. Add both to the beans and corn.
Peel the onion and the garlic cloves and chop them thinly. Add the remaining vegetables and mix well.
Drain the tuna, break into flakes and spread it over the salad. Drizzle the salad with chopped chives.
Squeeze one lemon, mix into the cooking oil and the corn water. Add chopped coriander and season to taste with chili and salt. Mix well and drizzle over the salad. Serve cool.