1. 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.
2. 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.
3. 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.
4. 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.
Wine Recommendation: The sweetness of the potatoes, the spice of the curry, and the saltiness of the ham all point toward gewürztraminer as the wine of choice. Try a not-too-dry example from Alsace or Washington State for a match made in heaven.