Pass formatted date to map?

We have a system task which should update the booking date as a map. When we use the expression ${now()} we get a unix timestamp, whereas we need it to be passed as a formatted human readable date. Since we couldn’t figure out how to do it in the expression alone (which we’re hoping there is a way), we created a groovy script to set the variable formattedDate with the format we need (this is all on the same system task). The issue is when the formattedDate variable is set with groovy, we get a workflow error that says: unknown property used in expression ${formattedDate}. Cause: Cannot resolve identifier ‘formattedDate’

Is there a way with the single system task to pass the formattedDate to the backend via the map?