Combine chick peas and black beans in a saucepan with 6 cups of water. Bring to the boil, reduce heat and simmer for 35-40 minutes until tender. Drain.
Heat oil in a large frying pan, add onion and garlic, cooking for 2-3 minutes until tender. Add cumin, coriander, oregano and chilli powder. Cook a further minute. Add canned tomatoes, water and drained chickrnpeas and beans. Bring to a gentle simmer and cook whilst stirring often for 6-8 minutes. Stir in seasonings and coriander.
Scatter each tortilla with lettuce, guacamole, tomatoes and onion. Top with a good spoonful of bean mixture, sour cream and cheese.