Region Union Problem

I want to know the easiest way to create a region from these two trimmed surfaces:

Here is my definition:

1- I know the problem is that "RUnion" component only works with curves.

2- I know that I can splitting curves and then join them to create the region; but I'am looking for a more straightforward solutions.
3- I know some plugins like clipper could do this, but I'm looking for more flexible solutions.

4- I tried Brep[] CreatePlanarBreps(IEnumerable<Curve>) in ghpython, but it doesn't work.