There is a trick to achieve what you want.
You can import your structured workout from TrainingPeaks into Tredict and from Tredict auto sync those workouts to Garmin.
This works pretty good for me!
Tredict supports the import of structured workouts in FIT format. On the other side this platform is also capable of syncing the training calendar with those workouts to Garmin. You just need to connect your Garmin account to Tredict for synchronization.