1.Make avocado cream. Mash avocado with juice and sour cream in a medium bowl with a fork until well combined, stir in onion and coriander. Season to taste.
2.Heat oil in a medium frying pan, shallow-fry tortillas, one at a time, until browned both sides and crisp. Drain on absorbent paper.
3.Spread tortillas with avocado cream then mashed beans, top with olives, cheese, tomato, lettuce and crab meat. Season with freshly ground black pepper.