This is fairly simple to do, Weexe actually was on the correct path just didnt give the entire information you seem need.
First create your 2 sprites and a Canvas holding your image you want inbetween.
Set "Order in Layer" to 2 and 0 for the 2 Sprites you want in the background or foreground. A higher number means it's in the front. All elements, including the UI will have to be on the same Sorting Layer.
Now, click your Canvas and set the Render Mode to World Space, this is needed so you actually get the option to go between sprites in the world. Cuz now you have the Sorting Layer and Order in Layer Option on your Canvas aswell. Set the Order in Layer to 1 and the Sorting Layer to the same as the 2 Sprites!
Note: If you can't find your UI Image note that it is actually super large in the scene, you'll have to heavily reduce it in size and position it the image(not the canvas). If you want to find it just zoom out alot and you'll start to see it ( Tip: if it's actually a small image you should activate the transform tool so you know where it's currently positioned ).
I just recreated this in a minute with example images, definitly works. If you have any further Questions just comment. I'll gladly help.