Cut sweet potato into long strips lengthwise, about 1/2 inch, square. You want your sweet potatoes to be roughly uniform in size so they all cook at about the same rate.
Place the cut sweet potatoes in a large cast iron skillet or on a baking sheet, and drizzle with oil, sprinkle with cumin, salt, and pepper, and toss to coat. Roast in 400° F oven, turning occasionally, for 30-35 minutes, or until crisp and browned outside and just tender inside.