Step 1Heat the oil in a large skillet over medium heat until shimmering. Add the onion and cook, stirring occasionally, until soft, about 5 minutes. Add the garlic, turmeric, coriander, salt, and pepper, and cook, stirring occasionally, for 2 minutes. Transfer to a 6-quart or larger slow cooker.Step 2Add the chickpeas, potatoes, and broth, and stir to combine. Cover and cook on the LOW setting until the beans are tender, 8 to 10 hours.Step 3Use an immersion blender to purée the soup until smooth in the slow cooker, or purée the soup in a blender, working in batches if necessary.Step 4Ladle into bowls, then garnish with a dollop of Greek yogurt, a squeeze of lemon juice, and cilantro.