Preheat oven to 400 degrees. Line a baking sheet with aluminum foil.
In a bowl, toss together the sweet potatoes with the olive oil until coated.
In a smaller bowl, stir together the salt, black pepper, cayenne, paprika, cumin, garlic powder, and cornstarch. Sprinkle the mixture over the sweet potatoes and toss to coat. Place the fries in rows onto the foil-lined baking sheet. Roast for 15 minutes. Turn the fries and roast another 5-10 minutes or until browned and cooked through (I like mine a little crispy on the edges). Sprinkle with cheese in the last 2 minutes of cooking and cook until the cheese is melted and bubbly. Taste for seasoning and season with more salt, to taste, if needed. Serve promptly.