Preheat the oven to 450. Coat two baking sheets with olive oil, cooking spray or line with parchment.
Wash and scrub sweet potatoes. Cut in half crossways and then cut into ½ inch fries.
Place sweet potatoes in a bowl and toss with the cornstarch, chili powder, cayenne pepper, and salt and pepper.
Add the olive oil and the juice of one lime to the potatoes and toss.
Spread them out on two cookie sheets. Toss on the spent lime halves (from being juiced) and cut the other lime into wedges and add them to the pan.
Roast for 20 to 25 minutes.
Remove from the oven and sprinkle with the cilantro and squeeze the lime wedges over the fries.
Notes
Sweet potatoes vary in size. If they are large, then 2 should be plenty fro 4 people. If they are smaller use more. You want about a cup of fries per person. This recipe uses less olive oil, if you want to use more you can up it to two tablespoons. You can increase the spices and add cumin if you'd like.