I don't have the answer to your question, but I don't see the connection between mindfulness and Zen to be as direct as you're suggesting. I've been highly influenced by a lot of the mindfulness writing out there, but Zen actively turned me off for a long time, because it's a lot of "deep" paradoxical puzzle/koan things, anecdotes that make no sense, emphasis on "enlightment" etc. Contrast that with a lot of modern day mindfulness stuff which is highly, highly influenced by Buddhism but basically extracts the most practical stuff, meditation practice, awareness of thoughts/feelings, recognition of egotistical cravings, acceptance of impermanence, etc.