Same boat here. B737 pilot. I also need to get my PBN in my license for my 737. You can actually combine it with your OPC or LPC. We as MPA Pilots do not need to do an extra training session but we do need to do skilltest with few approaches in Sim.
I almost made mistake to do it on C172, which then will be utterly useless of course for my 737.
So dont do it on SEP MEP FNPT or actual aircraft, but try to combine it with your OPC or LPC.
Most 320 sims should be certified to do PBN. Also make sure you have had your Theoretical training for PBN. For instance my company provides via an CBT which my CAA recognizes.
Good luck and keep us posted.