I had hoped to use another tscn file to define the tab, and then just insert it in and wire it up, but Couldn't get that working, loaded fine, but instancing it spit out:
At: scene/resources/packed_scene.cpp:98
WARNING: instance: Parent path './RandomPortrait' for node 'minmatch' has vanished when instancing: 'user://mods/randomportraits/options.tscn'.
Worked fine to create a tab in code, add the texture (duplicate dit from one of the other tabs), and then start adding my own checkbox's and labels. It's just tedious laying things out.