Step 1
Bring a large pot of generously salted water to a boil. Add the potatoes and cook until tender, about 45 minutes. Drain the potatoes and set aside until cool enough to handle. Peel and coarsely chop the potatoes, then transfer to a large bowl and set aside.
Step 2
To a medium skillet over medium-high heat, add the oil; when hot, add chiles and cook, stirring frequently, until lightly browned, about 1 minute; remove from heat.
Step 3
Transfer the oil and chiles to a blender, then add the yogurt, tahini, curry powder, lemon juice and zest, salt, and black pepper; purée until smooth. Pour the dressing over the potatoes and stir in half of both the cilantro and scallions. Garnish with the remaining cilantro and scallions just before serving.