What is the primary vegetable used in the cheese fries topping?

The primary vegetable used in the cheese fries topping is green onions. Green onions add a fresh, mild onion flavor that complements the richness of the cheese and the crispy texture of the fries. They provide a pop of color and a crunchy bite, enhancing the overall taste profile of the dish. This choice aligns well with common culinary practices where green onions are frequently used as a garnish or ingredient in various appetizers, bringing lightness and freshness to heavier items like cheese fries. The other vegetables listed do not typically serve as the main topping for cheese fries, which solidifies green onions as the correct choice.