Vegetarian Mongolian Beef is a meat-free alternative that still captures the essence of the original dish. Instead of beef, this version uses tofu or seitan as the main protein. The tofu or seitan is marinated and stir-fried with the same flavorful sauce and green onions. The result is a delicious and satisfying vegetarian dish that is packed with flavor and texture. Serve it with steamed rice or noodles for a complete meal.