Vegetarian Mongolian Beef is a meat-free version of the dish that is perfect for vegetarians or those looking to incorporate more plant-based meals into their diet. In this recipe, tofu or seitan is used as a substitute for the beef. The tofu or seitan is marinated in a mixture of soy sauce, hoisin sauce, and cornstarch, and then stir-fried with green onions and a savory sauce. This vegetarian version still captures the essence of the original dish and is a delicious and satisfying alternative.