Having a low body fat %
Shows more of the penis.
But for actual growing i would say that a diet with a vast amount of minerals, vitamins. Well hydrated and low on junk (basicly the same thing as what you would do to regrow a wound) would be most beneficial.
Oh and remember a cardio regiment aswell.
Heavy lifting is known for increasing test levels massively but i dont know if it would be enough to help growth og the penis