Why my phone is stuck on a backlit black screen?
Although I've never had a Lenovo device, I have accidentally deleted my OS and recovery before.

Are you able to boot the phone into 'Download mode' (I would love to post a guide for you but, after a quick Google I couldn't find one)?

Download mode should still be available (it's used by the manufacturers to install the OS in factory) and hopefully you'll be able to connect your phone to a computer and re-flash the firmware.