Awakening the heart with Zen Master Thich Nhat Hanh (8/14/2011) Chanting 1-3
The words are simply “Namo Avalokitesvarya”.
You can think of “Namo” as meaning “praise” or “adoration” and Avalokiteshvaraya is the name of the Boddhisattva of Compassion. They are singing the name in each syllable and the effect is that it sounds like lyrics. SOURCE
NB The first time you might want to start about 8 mins 30 seconds into the video