Any ideas on how to fix this gap between my cabinet and wall?

It's a bit of a long story but someone tried using spray foam to fill the hole around where my sink's plumbing goes through and it seems like it essentially expanded too much and causing the paint to tear.

I was thinking maybe I could get some rigid insulation cut it to size, stick it in there, and spackle over it followed by painting it. I would probably cut the rest of the paint to the top because it looks as if it is going to tear eventually and it's at an angle.

Any suggestions?

The gap is close to an inch in size.