For a vegetarian option, substitute vegetable broth for chicken broth and omit the chicken. Adjust the amount of five-spice powder to suit your taste preferences. Feel free to add other vegetables like snow peas or water chestnuts for added texture and flavor. If you don't have Thai basil, regular basil can be used as a substitute, although the flavor will be slightly different. Ensure the cornstarch mixture is completely smooth before adding it to the soup to prevent lumps.