Is it possible to make a ZIP that can be flashed onto a device to add a bundle of applications (.apk files) to the /system/app directory such that it can be flashed after the OS (e.g. CyanogenMod) in a similar way to other bundles such as OpenGApps ?

I've seen things like the ZipMe app but I'd really like to do this on Linux where I have the desired apk files in a directory. I'd like to do this by hand if possible to that I can understand the ZIP's contents.