As with the Basic Situation and Variation Two, Zack is guilty of theft by deception. Preliminarily, he intentionally loaded up his salad for the purpose of concealing the steak on it. But Zack's moral culpabilty here exceeds even that of Variation Two because, here, Zack affirmatively misrepresented the nature of the salad when asked.
Zack's greater moral culpability might merit greater punishment in the unlikely event the full facts were to come to light. A decent likelihood exists that Zack's misdeed will never be discovered. If all the circumstances were discovered, however, Zack's misrepresentation would be a fact that would increase the likelihood of a conviction.
For reasons indicated in our Variation One discussion, the likelihood of a prosecution is small. As in that discussion, however, the governing principle applies when the amount involved is orders of magnitude greater. In those situations, Zack's misrepresentation would assist the prosecutor in nailing record of a criminal conviction onto Zack.