Avatar real time Facial Expression "Inspector"/Camera

Hello,

I found those avatars made by a User called Thunder (they also have an avatar world)
They have a really neat feature which shows your Avatar in a little Camera above your Mute Icon.

Since im somewhat clumsy with my index controllers this feature helps me alot making sure i actually do the right gestures. So i would love to add this to my own avatar.

Does anybody here know how this is done? Or if someone already made a prefab for it?
I would appreciate a nudge in the right direction, ill probably figure out the rest myself.

All help is appreciated.
Thanks in advance!

Greetings
Sweeny