If using dry chickpeas, soak for at least 4 hours or overnight, rinse and cook till soft and mushy. Drain and reserve some liquid.
Puree the chickpeas along with garlic.
Cool and add tahini and lemon juice. Taste and adjust sourness with lemon juice and season with salt. Add the reserved liquid to loosen up consistency if necessary.
Garnish with olive oil and black olives.