Q. (Re- questions 2122-23). To clarify – regarding the opinion of the Vilna Gaon that it is a mitzvah to eat matzah all seven days of Pesach, does this meant that one fulfills a mitzvah with every kezayis consumed, or that one fulfills one mitzvah per day that he eats matzah?
A. He fulfills a mitzva every time he eats a kezais as mentioned; “Gilyonei Hashas (Pesachim 38a) compare it to seating on the suka on the rest of the Yom Tov.”
Important to note that, as mentioned, it is not only the Gaon’s opinion, others also agree such as the Rokeach (291), Chezkuni and Eben Ezra (Mispotim 23: 15), Chasam Sofer (191) mentions that so is the opinion of the Rosh and the Ran, et. al.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit’a