When I use creature swap on MY pyramid turtle and I destroy it as a result of battle when it's in my opponent's control, who gets the effect? me or my opponent? who gets to summon a zombie from thier deck?

Use the search function next time as this question has been asked tons of times already.

If Monster's that activate when sent to the graveyard (Sangan, Mystic Tomato, Pyramid Turtle, Nimble Momonga, etc) are on your opponent's side, YOU will still get their effect as they are sent to YOUR graveyard and not to your opponent's.

You get to summon a zombie.... Then you can attack with it too! :)