In a large saucepan, soak garbanzo beans in water to cover by 2 inches for at least 8 hours, or overnight.
Drain, rinse well, and return to the saucepan, Add 2 quarts of water and simmer, covered, for 1 hour. Add salt and simmer 15 minutes more or until tender. Drain beans and set aside to cool.
Bring a medium saucepan of water to a boil. Cut tops off bell peppers and remove core and seeds. Blanch peppers in boiling water for 1 minute. Drain well. When cool enough to handle, dice peppers.
Peel and slice onion and soak in a bowl with ice water for 10 minutes. Drain, pat dry, and dice.
In a large bowl, combine garbanzo beans, diced peppers, and diced onion. In small bowl, whisk together lemon juice, vinegar, oil, coriander, cumin, and garlic. Add salt and black pepper to taste. Pour dressing over vegetables and toss gently. Serve chilled.