For the Leche de Tigre, first squeeze the limes and puree the juice with a pinch of salt, garlic, chopped coriander and 2 tablespoons of finely chopped fish.
Cut the remaining cod into hazelnut-sized pieces and lightly salt. Cut the onion into strips and fold into the fish. Finely dice the avocado and add it along with the Leche de Tigre. Mix everything together well and season with salt, pepper and freshly chopped coriander. Let it steep in the refrigerator until the fish turns white and firm. The acid of the Leche de Tigre cooks the fish.