Drain beans into colander and rinse until water runs clear. Allow to drain well.
Whisk together dressing ingredients.
Put garbonzos and dressing into a sealable container. Shake a few times to distribute marinade. Allow beans to marinate in dressing one hour or longer.
In the meantime, dice the tomatoes, place in colander with a small amount of salt and let tomatoes drain 10 minutes. If using avocado, peel and dice the avocado and toss it with 2 teaspoons of lime juice.
Slice green onions and chop cilantro.
Combine marinated beans with dressing, tomatoes, green onion and cilantro. If using avocado, fold in gently until well combined. Season with salt and pepper to taste and serve immediately.