Sending Images across Unity to iOS Bridge

I'm building an app that has a heavy UI Layer built in UIKit.

As part of the UI, we built a messenger system that is very similar to whatsapp, and uses images of the users' avatars for profile pictures. These avatar images are rendered in unity and stored as sprites on the unity side of the bridge, but we need to send them over to the iOS side in order to display in the UI.

What's the most efficient way to do this?