How to tell your vegetarian friend that you don't want to discuss that while eating?

I have an acquaintance I get together with occasionally. She is a dedicated vegetarian and has made it her pet project to convert me from my omnivorous habits. I’m fine with it all really….except for one tendency of hers: she brings up the darker side of the meat industry while I have a half eaten hamburger or hotdog on my plate.

I know its an issue and one worth discussing…and I am happy to discuss it outside of mealtimes. So, what’s a polite way to tell her to “shush it” during lunch (preferably without destroying the relationship)?”