Hi Daryl,
Before I begin this response. I am no expert so please take this example as my understanding of how an extension UI should be built for Omniverse :)
I am building a custom extension for this. I started with exploring the extensions that come with Omniverse, understanding how they structure the entire package together. Took a couple of days to get the gist of it and now exploring the details of it. I have attached a minimal UI extension to this reply if that interests you. Simply clone this repo to a Extension search path (I prefer: “…\Documents\Kit\shared\exts”) on your machine and try it out in one of the Omni Apps.
Hope this helps :)
Regards
Tanay Dimri