In a large bowl, combine 1 can of black beans (rinsed and drained), 1 ripe peeled and finely diced avocado, 200 g finely diced white onion (rinsed briefly under hot water in a sieve to soften its bite), and 300 g finely diced tomatoes (flesh only, seeds discarded).
Add 3 tbsp roughly chopped coriander greens, 1 tbsp freshly squeezed lime juice, 0.5 tsp sea salt, 0.25 tsp chilli powder, 0.25 tsp ground cumin, 1 pinch black pepper, and 1 tbsp fruity olive oil. Toss gently — do not mash the avocado.
Cover with cling film and serve within 2 hours — the avocado will begin to darken after that.