For those following a vegetarian or vegan diet, you can still enjoy the flavors of Mongolian Beef with this vegetarian version. Instead of beef, this recipe uses tofu or seitan as a protein substitute. The tofu or seitan is marinated in a soy sauce-based sauce and then stir-fried with vegetables like mushrooms, bell peppers, and onions. The result is a delicious and satisfying vegetarian dish that captures the essence of Mongolian Beef.