I am licensed as a Private Pilot, Airplane Multiengine Land, what do I need to do to be able to fly as PIC in a Single Engine Land aircraft?
No, you cannot. Just like an ASEL doesn't give you the ability to fly an AMEL, if you have an AMEL that doesn't give you ASEL privileges.
Adding the ASEL shouldn't be that hard though, especially if you've done a majority of your training in one. You will still need to take a check ride.