According to the halachic sources one may bentch once a kezayis of bread has been eaten within 3,4 or 9 minutes.
Time Limit (min) – How much time does one have to consume the kazayis amount: The consensus among most poskim is that the time of “Kdei Achilat Pras” is 4 minutes, but there are minority opinions that range from 2-9 minutes, and in some circumstances it would be advisable to be cautious for these minority opinions.
Say one is having a soup with a slice of bread the size of a kezayis. Unless he eats very quickly, it would be hard to eat the whole kezayis within the time limitations above. Does this mean that if one ate the meal with the soup but took longer to finish the kezayis of bread then he doesn't need to bentch? Or perhaps you can count the additional non-bread food towards the "satisfaction" criteria that requires one to bentch (veachalta vesavata uverachta).