ya olduğun gibi görün yada göründüğün gibi ol

 either be as you seem or seem as you appear

something like that

 either exist as you are, or be as you look.

Note : this is a quote of Rumi. [ Mevlana Celaledding Rumi ] , great thinker lived in Konya centuries ago.

All the best men come from Konya

could it also mean....be who you are?

 yes, thats possible,

ya olduğun gibi görün yada göründüğün gibi ol

  - be who you are

  - act as you are

  - behave as you are

  Moral of the story is , dont wear mask, dont act like somebody else, be yourself. Be honest person.

 I don´t think so. This has a different meaning in English. Like "be yourself" or "be true to yourself". It would be olduğun gibi ol in Turkish.

Tunci is right that Mevlana´s words are against being two-faced or hypocritical.

e.g. don´t appear to be nice and then turn round and stab people in the back.

That´s 100% true! I am a Konya man from birth!  

öyle mi , well I never, knock me down with a feather