ls -t | grep ".Numbers"
cd ~/Desktop; open "`ls -t | grep .Numbers | head -1`"
I'm amazed, didn't think that I would manage it but I figured it out in about 30 minutes of trial and error.
And believe me, there were lots of errors
Code:cd ~/Desktop; open "`ls -t | grep .Numbers | head -1`"
It's a bit picky about the file ending, the file extension needs to be visible in the finder and capitalization matters.