Settings app has disappeared HELP

1. My settings app has disappeared from my Nexus 5. I was running Lollipop with an unlocked/rooted phone (done with the excellent Nexus root toolkit).

2. I tried to factory reset the phone but the settings app is still missing. I cannot install or sideload anything because everything requires USB debugging to be turned on, which requires me to change the Settings!

3. ANY SUGGESTIONS?

Thanks in advance!