Add the sweet potatoes to a large pot of cold salted water. Bring to a boil over medium-high heat and cook the potatoes until tender, about 15 minutes. Drain the potatoes and cool in a colander. Transfer to a large serving bowl.
In a separate bowl, add the pickled onions, yogurt, cilantro, lime juice, curry powder, lime zest and some salt and pepper, and whisk to combine. Pour the dressing over the potatoes and thoroughly mix. Serve immediately or refrigerate for 1 hour for the flavors to meld.