Birkat haMazon for eating small quantities of bread at a meal

Hi,

One who ate a full meal, but only ate less than an olive-sized amount of bread at the meal, does not recite Birkat haMazon. One should only recite the closing berachah associated with those foods for which he consumed the threshold amount to require that berachah.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 4:41)

Have a great day,
Mordechai