Unfortunately, this doesn't really seem possible. Angular and Zen, being frameworks, both pretty much expect to have total control of what goes on in the page and will only get in each other's way. In particular, Angular tags don't play nicely with Zen's XML model. The good news is that you don't have to rewrite the whole application at once, and can start by writing new pages using Angular and creating REST APIs as needed, while still being able to keep the old Zen pages that you don't want to rewrite. You can even try to switch the Zen-based parts of the site to using css-based layouts rather than Zen's default table-based layouts with hgroups and vgroups to make the old and new pages look more similar.