Probably the bridge tool would be fastest, but you could do it with edge extrusion/weld or putting a plane there and then welding verts. Bridge tool is probably the closest you're going to come to a "magic fill this shit" button, everything else is more work, but the bridge tool isn't going to do that all in one click,…
2 methods in modo really 1. Select 2 edges(or more), bridge. if your # of sides are even, you can select a bunch of edges and bridge to get perfect quads etc. by # of sides varied a bit more than i liked so i needed some tris in there 2. Select vertexes and make poly! In modo this is P on the keyboard, im sure other apps…