Hi,
The Field of View of the ZED Mini camera is smaller than the Field of View of the HTC headset, which creates those black borders.
If you want the image to fill the whole screen, you can scale up the planes where the zed images are projected (). However, this will obviously distort the image.
You can also find another solution proposed by a User on Github, using XRDevice.fovZoomFactor (https://github.com/stereolabs/zed-unity/issues/157).
Best,
Benjamin Vallon
Stereolabs Support