In a deep, heavy-based pot, cover the chickpeas with 6 to 8 cups cold water. Add the turmeric, bay leaves, yellow onion, and 1 tsp. salt. Over high heat, bring to a boil; reduce to a gentle simmer, skimming any foam that rises to the surface. Cover and cook until the beans are tender, about 90 minutes; let cool in the broth.
In a heavy-based pot, cover the potatoes with salted water. Bring to a boil over high heat and cook until tender, about 20 min. Drain. When cool enough to handle, peel and cut them into small cubes.
In a small bowl, combine the yogurt and sour cream. Add the ginger, cumin, fennel, and chile. Mix well.
Drain the chickpeas, discarding the onion and bay leaves. In a serving bowl, combine the chickpeas, potatoes, cucumber, and red onion. Mix in the yogurt dressing, cilantro, and mint and combine well. Let sit for 15 minutes. Taste and add more salt if needed. Serve at room temperature.
The beans can be cooked a day ahead (in fact, the flavor and texture will be even better). Cool the beans to room temperature then refrigerate in their cooking liquid; bring to room temperature before assembling the salad.