We do kokyo-ho, which is breathing practice. It is not 'zazen' per say, but could be considered some type of meditative practice. (Breathing is a slow controlled fashion, clearing the mind, entering contemplative thought.)
It's usually done at the end of class but depending on the time or season can be done both at the beginning and end of class
One thought we use is:
Breathe out so that your breath travels infinitely to the end of the Universe; breathe in so that your breath reaches your one point and continues infinitely there.