Make plugin override a file in my theme

Hi hoping somebody can point me in the right direction.

I have a wordpress theme, with a file inside the theme called custombar.php

I also have a blank plugin, with a file inside called custombar.php

what im trying to do is make it so when i upload and activate the plugin, and custombar.php is called from the theme, it will use the custombar.php from the plugin folder instead, overriding the original file without having to change any code in my theme.

thanks in advance