How to Make It
Bring a medium pot of salted water to a boil. Add the sweet potatoes and boil until just tender, 5 to 10 minutes. Drain the sweet potatoes and transfer them to a large glass or stainless-steel bowl.
In a small frying pan, heat the 1 tablespoon oil over moderate heat until it is hot but not smoking. Add the almonds and curry powder and cook, stirring frequently, until fragrant, 1 to 2 minutes. Transfer the nuts to the bowl with the sweet potatoes and add the ham and scallions.
In a large glass or stainless-steel bowl, whisk the vinegar, salt, and pepper. Add the remaining 2/3 cup oil slowly, whisking. Toss half the dressing into the sweet-potato mixture.
Toss the lettuce into the remaining dressing. Put on plates and top with the potato salad.
Variation The curried nuts and ham make great complements to sweet potatoes, but they're excellent with regular boiling potatoes, too.