Combine the chickpeas and baking soda in a large bowl or pot and cover with at least double their volume of water. Transfer to the refrigerator and soak for 18 hours.
Drain the chickpeas and rinse thoroughly in cold water. Place the chickpeas in a large pot with the whole head of garlic and cover with water. Bring to a boil, and then reduce the heat to low. Simmer the chickpeas over low heat until very tender, about 3 hours. Drain, reserving 1 cup of the cooking liquid and 1 cup of whole chickpeas. Discard the garlic bulb.
Combine the remaining chickpeas, the sesame paste, grape seed oil and lemon juice in a food processor and puree to a smooth, creamy consistency, adding reserved cooking liquid as needed. Season with salt and cumin.
For the tehina:
Combine the sesame paste, water, lemon juice and garlic in a blender and blend at high speed until smooth. Blend in the olive oil. If the puree is too tight, adjust the consistency with additional warm water. Season with salt and cumin.
Spoon the hummus into a large shallow bowl. Create a well in the center, using the back of a spoon, pushing the hummus to the edges of the bowl. Toss together the reserved whole chickpeas with the tehina in a mixing bowl and adjust the seasoning if necessary. Spoon the dressed chickpeas into the well in the center of the hummus. Garnish the hummus with the olive oil and chopped parsley. Serve immediately.