Open up System Preferences and click on Keyboard & Mouse. Select the Keyboard Shortcuts tab, and click on the plus at the left to add a new one. You'll want to type in Zoom and whatever key combo you wish--I like shift-cmd-M.
Should look something like this:

Save that and open a new terminal window and give it a go. It will of course work in whatever app you can zoom in, I just find I use it in terminal and sometimes my browser almost all the time.
Enjoy!
