Also rabosai, consider this gem: In a compendium on chagim, I found a quoted maamar of the Chazon Ish regardng kezais. He says that Hakodosh Baruch Hu knew we would be subject to exiles and wanderings, thus in his mercy, he gave us natural signs for the shiurim. Hence a kzayis is the size of an olive in every time and every place relative to that place. The responses to this fell into two basic groups: Group A) that not what he said, thats not what he meant, he said it but not lhoros, he didnt mean it that way. he meant it but didn’t say it …..
Group b) took it and reasoned that the largest possible olive in our times is the the shiur (California Colossal?) and so a Kzayis is about 20 ml or the (outside)volume of two soda bottle caps, or a small size match box, and this is the shiur for all mitzvos and bracha aharona.
Now if we go with group B, one slice of pizza is clearly more than two or three kzaisim, and for the deah that says that kvias seudah is based on quantity, One slice shouold be hamotzi and benching.