No, because it's traditionally made with beef stock. My recipe for French onion soup in the crock pot also includes Worcestershire sauce, which contains anchovies. However, you can easily make a vegetarian version with a few easy swaps! Replace the beef stock with vegetable stock or mushroom broth, then substitute soy sauce for Worcestershire (or leave it out entirely). The flavors won't be as deep, but it'll still be delicious!