I've wiped my Nexus 7 but can still access TWR?

Hi there,

Whilst in Team Win Recovery I managed to completely wipe my device of the OS and all my data. Thankfully I had backed up my media, but not my OS which at the time was Slim Bean.

I can now manage to boot the nexus into fastboot and also into TWR, however I can't seem to push the Google image across. I've tried connecting the device via ADB through the sideloader available in TWR but it isn't being picked up on my pc running windows 7.

I can however see the device connected through the nexus root kit when I put it into fastboot, but there isn't any option to push files through root kit in this way?

Please could someone help me with this?

Many Thanks!