Eating a Kzayis in Bliah Achas

The Mishnah Berurah (476:41) writes that l'chatchilah it is preferable to eat the k'zayis matzah on Pesach in one swallowing. I heard that the Chofetz Chaim himself was makpid on this halacha even on Sukkos, to eat the k'zayis of bread in the sukkah in one swallow.

Presumably, the idea is that anytime there is a mitzvah of achilah (achilah always being defined as a k'zayis) it is best to do the mitzvah all in one shot.

I heard a question asked on this: Why not say in all the Seudos of Shabbos that one should eat a k'zayis in one shot?

One possible approach may be to use the lomdus we discussed in our two previous posts. The mitzvah to eat the meals of shabbos is not really a mitzvah of a maaseh achilah per se. It is merely a mitvah of oneg shabbos, accomplished through eating. However, the mitzvah of eating matzah and perhaps eating in the Sukkah (acc. to some rishonim) is a mitzvah specifically of achilah. Therefore the Chofetz Chaim was makpid to eat, in those instances, in one bliah.

This is the suggestion I heard. Perhaps another explanation is that the gemara in Sukkah 27a has a gezairah shaveh between the chiyuv to eat matzah on the 15th of Nissan and the chiyuv to eat in the sukkah on the 15th of tishrei. Perhaps it was this equation that motivated to Chofetz Chaim to be machmir the same chumrah on both days.