Is this the best way?

 From:  TpwUK
5491.3 In reply to 5491.1 
Hi Cube, if you are playing with version 3 beta (the latest one) then there is a more variable network surface option. Draw a curve using the three point curve option, draw it from the middle of the top edge to the bottom edge mid point and then adjust its curvature to suit, then select the four outer edges of the hole, then the new curve you just did, and click network surface.

Hope that helps