From mesh to polysurface to surface

Hello how can I turn this mesh into a single surface that is not made up of multiple polysurfaces. I have tried converting it from mesh to surface, or subD to surface but it always gives me polysurfaces and when I try lunchbox on it, each surfsce segment is treated as one rather than treating the entire form as one surface. How can I make this entire segmnented surface, one whole surface?
QUESTION_MESH2SURFACE.3dm (5.7 MB)
QUESTION_MESH2SURFACE.gh (4.9 MB)
QUESTION_MESH2SURFACE 6.3dm (5.1 MB)

I dont want the lunchbox to apply grid like this. Each surface is treated as an individual within the entire form.