Preheat the oven and bake the curly fries according to package directions.
Meanwhile, toss the cheese and cornstarch together in a small saucepan, then add the half-and-half. Cook over medium heat, whisking constantly, until melted and smooth, about 5 minutes. Add a little more half-and-half to loosen the sauce if needed.
Put the curly fries on a serving plate. Drizzle with the cheese sauce and ranch dressing and sprinkle with the bacon, onions and cilantro. Dot or drizzle with sriracha to taste.