Denver omelet, an omelet with ham, onion, and bell pepper; cheese is sometimes included. Historians have speculated that the dish was originally served on bread as a sandwich, created by 19th-century cattle drivers in the American West or by Chinese railroad cooks as a sort of transportable egg foo yong. At some point a breadless version was developed, and it became known as the Denver (or western) omelet. The sandwich variety, called a Denver (or western) sandwich, is still common.