Using a 16oz jar of Tahini seems like a lot. Are you really supposed to use the whole jar?

I looked in the Israeli Soul book, and that is correct. You don't have to use all of the tehina sauce. You can reserve it for dressings, to serve with roasted vegetables.
It makes four one-cup servings, so it is not as much as it sounds--but more than the recipe in the Zahav cookbook if memory serves.