Do you clip his toenails so he can't plow deep scratches. The tiny point on the end of his claw is removed. Doing this is important for your relationship with him.
You can't foretell what an iguana will consider a treat.
I've had good luck with bits of banana, about one 1/2 tbs/treat on the end of a fork held under his nose. Pizza crust is a good one, and of course the amount offered is small and insignificant to his weekly nutrition. 1/2 inch square is good. He might ignore treats at first, but keep it up. When you find something that he lunges for, or snaps up, you have a great socializing tool.