Combine the chickpeas with baking soda and cover with water. Simmer for about 30 minutes, until the chickpeas are really mushy. Strain the chickpeas, but reserve the cooking water.
In a small pan, cook garlic cloves over low heat for about 20 minutes, until tender.
Transfer the chickpeas and walnuts to a food processor. Add lemon juice cumin and cooked garlic. Blitz until smooth (may require a few minutes). Add the cumin and olive oil, and and blitz again. At this point, check for consistency and seasoning. Add salt to taste, and add reserved cooking liquid, a bit at a time, if it's too thick, until you achieve the correct consistency.
Serve with bread, crackers, and vegetables. Also makes a great sandwich filling.