Yes, there are several alternatives to Worcestershire sauce that can be used to flavor the filling of Shepherd's Pie.
Soy sauce: Soy sauce offers a savory, umami-rich flavor that can substitute for Worcestershire sauce. Use it in equal parts or adjust to taste. Balsamic vinegar: Balsamic vinegar adds a slightly sweet and tangy flavor, similar to Worcestershire sauce. Start with a small amount and adjust to taste. Miso paste: Miso paste provides a complex, fermented flavor that can enhance the richness of the filling. Use it sparingly, as it's pretty potent. Fish sauce: Fish sauce adds a salty, savory depth of flavor to dishes, similar to Worcestershire sauce. Use it in moderation, as it can be quite pungent.