Show tar.gz files but tar.gz is already inside a tar file

I want to see a tar.gz files that are inside a tar file.

So I have a tar file that has a tar.gz file inside and I want to see the tar.gz files without extraction my tar and my tar.gz.

So to explain more, inside my tar I have a tar.gz, File.tar -> File.tar.gz. so I need to see the files inside my tar.gz but my tar.gz is already inside my tar, and that without extracting my tar and also my tar.gz.

I tried this but doesn't work : tar -xvf File.tar File2.tar.gz | gtar -ztvf -

Can you help me with this?