Default soft bricked!?

So I soft bricked my Nexus 7 (flo).... I have root access and I have TWRP installed still... just no files or anything... I could easily fix this if my PC had Windows but currently I only have Ubuntu. All the fixes and guides are for Windows and I need some help trying to sideload a rom in Ubunutu... I tried to adb sideload a rom but only get this error on my PC "cannot read sideload" . Any suggestions on what I can / should do?