@jabongzki Hi and welcome to the Forum.
You do not have to completely erase the disk if you do not want to. You could shrink the existing partion (assume just one) and create space for a second primary partition for ZorinOS.
When Installing Zorin, use the "Something Else" method, which allows you to select that specific drive.
It has been done before, see this: Install Zorin on 2nd physical HD
Also from the old Zorin Forum: Setting up for Dual Hard Drives [Solved} - Old Zorin Forum archive