Wash beans and cover with 4-6 cups of water. Soak for at least 4 hours. Discard water and replace with 4 cups of fresh water and 1½ teaspoons salt. Bring to a boil over medium heat. Reduce heat to simmer and cook for 1½ -2 hours (add more water if needed).
While beans are cooking, prepare the cucumber, scallions, green pepper, carrots, celery and tomato. When the beans are tender, remove from heat, drain, and cool. Add the vegetables and olives to the beans. Adjust salt and pepper. Cut the lemon in half. Squeeze both halves into the bean mixture. Add the olive oil and cilantro and toss gently.
Soak garbanzos for at least 4 hours before cooking.