Place the garbanzo beans into a large container and cover with several inches of cool water; let stand 8 hours to overnight. Or, bring the beans and water to a boil in a large pot over high heat. Once boiling, turn off the heat, cover, and let stand 1 hour. Drain and rinse before using.
Place the soaked garbanzo beans into a large saucepan and cover with several inches of water. Bring to a boil over high heat, then reduce heat to medium-low, cover, and simmer until the garbanzo beans are tender, 1 1/2 to 2 hours. Once cooked, refrigerate the beans and liquid until cold.
Drain the garbanzo beans, reserving the cooking liquid. Place the beans and 1/2 cup of the reserved cooking liquid into a blender, and puree until a smooth paste forms. Add the pumpkin puree, lemon juice, olive oil, tahini, garlic, cinnamon, nutmeg, and allspice. Cover and puree again until smooth. Use additional cooking liquid as needed to achieve a smooth consistency. Season to taste with salt.