To make a statement like this you have to start making distinctions between God's will and his plan.

It's not appropriate to say that it was God's will for them to eat the forbidden fruit, when he expressly says otherwise, and we know that he is too holy to lie.

But we know that salvation through Christ was ordained from before the foundation of the earth (Ephesians 1, I think); therefore, we must recognize that God had an uber-plan that accounted for the reality of disobedience so that he could demonstrate his justice and mercy.