Even with all the pom and circumstance of the opening of the show, I think the match ups are pre determined (I don't think the challenger is actually selection the competition on the spot).
Also, I think before the battle the challenger and the iron chef are given 3-4 possible secret ingredients which they would prepare for all of them. When the "secret" ingredient is revealed, they have some idea of a menu.
Also I think they only have to have one of each menu item plated before the buzzer rings.
What are other thoughts, behind the scenes ideas? rants, raves etc?