How to automatically zoom on Flutter WebView

I would like to know how to automatically zoom on Flutter WebView.

I know the user can manually zoom on the WebView content, but I would like to control it from the start because when I put the emulator in portrait mode the informations in my WebView are too small for the user to read :

I tried to increase the WebView width to make it larger and so that it would automatically be zoomed and the user could use horizontal scroll to read it.

 child: WebView(
                          zoomEnabled: true,
                          initialUrl: Uri.dataFromString('<html><body><iframe src="webpage_url" width="1920" height="700"></iframe></body></html>', mimeType: 'text/html').toString(),
                          javascriptMode: JavascriptMode.unrestricted,
                        ))

This works well with the IFrameElement that I use for the web version of my app (WebView isn't supported by Flutter Web nor is IFrameElement by the android emulator)

IFrameElement _iframeElement = IFrameElement();
    _iframeElement.height = '750';
    _iframeElement.width = '1920';

Here(web version of my app), the iframe is automatically zoomed accordingly to the width and I height I defined for it :

How do I achieve that using WebView ?

Thanks for helping.