IMO, there is no compliant way to hide the low voltage wires in a wall for puck lighting and most other LV systems. I have not found a suitable way to be compliant except to install the transformer in the upper cabinet and leave it exposed under the cabinet.
There are some systems out there are approved for wires in the wall but it is an entire system. Read art. 411 esp. 411.3, 411.4 and 411.5