Heat olive oil in a large skillet. Add onion; cook and stir until translucent, about 5 minutes. Add garlic; cook and stir until fragrant, about 2 minutes.
Stir garbanzo beans, taco seasoning, and cumin into the skillet. Pour in chicken broth and cover. Bring to a boil; reduce heat to low and simmer until soft, about 10 minutes. Mash mixture with potato masher. Season with salt and pepper.
Pull lettuce "cups" out of the center of each half. Fill with garbanzo bean mixture. Top with avocado, tomato, and olives.
