If you're asking people to choose an entree before hand, you don't need to give the full recipe, but enough detail to make a choice. Using your example, if you would list chicken parmesan as entree parmesan, or if it were basil pesto beef with cashews would you list basil pesto entree with cashews? You don't have to give a menu beforehand , but if you do, it is rather important to list key ingredients in the description. In your case, the tofu is a key ingredient and should be listed.
As an aside, if you are thinking that you might need to hide the vegan nature of the caterer from your guests, that should be a huge red flag that it may be the wrong choice for this event. Granted, your event, your choice, but picking something that you think will be so poorly received by your guests that you need to hide it from them is probably not a great idea.