i haven't read anyone else's comments. so i might be saying the same thing for 14th time, but i think this is a fold. i agree his cbet size is shitty but it's 5nl, i wouldn't expect my opponents to understand good strategic betsizing very well. if you had a read on this guy that undersized OOP cbets are a typically weak range then i'd definitely start opening up and bluffing him (though on this board i'd prefer to use hands like XhXh, KQ, 89, AQ etc which have some equity against his calling range - your hand is basically dead to two outs every time you bluff this flop and are called)

without reads, i think the best plan is ABC poker at 5nl. i imagine that's what most other people are going to have said ^^ up there.