It seems that the ZKGrails plugin does what you want.
It enables you to port the ZUL pages you developed in ZK to Grails. In particular, you would extend the class GrailsComposer
(which in turn extends from ZK's GenericForwardComposer
) in order to autowire your ZUL UI components to Grails event handlers.
This ZKGrails tutorial shows how to port the ZK's Load-On-Demand program to Grails.