Is there any source within the halachic literature that says that if there is a group of people who have eaten a meal together and some did not eat bread, everyone may/should be included in the zimun and say Birkat HaMazon together? (or put it another way, if one did not eat bread, but ate the amount of food which would satisfy him, may he still say Birkat HaMazon and answer the zimun with those who are benching?)
Please send any sources .
Somebody who did not eat bread cannot recite birkas ha-mazon, but only the relevant after-berachah, depending on what he ate.
However, if there are at least two people who ate bread, a third person who did not eat bread can join them to complete a zimun.
Zimun applies only for birkas hamazon, and not for other berachos acharanos (after blessings).Thus, at least two people must have eaten at least a kezayis (approximately half a slice) of bread for a zimun to be possible.
However, the third person may answer the zimun after having any food or drink, other than water (Shulchan Aruch 197:2). However, some rishonim write that this is the case only with regard to turning a regular zimun into a zimun of ten (zimun that includes the Name of Hashem). According to these authorities, if two ate bread and one ate fruit, they cannot perform zimun (ibid.).
To stay out of doubt, Sephardim avoid the situation where two who eat bread together invite a third to eat something other than bread (other grain products are a question). If it happened that two ate bread and one ate something else, then they should do a zimun (ibid.). The minhag among Ashkenazim is that if the third prefers not to eat bread, one may give him something else to eat or drink and invite him to join the zimun (Mishnah Berurah 197:22).