Q. Can you make a seudas mitzvah just with mezonos?

A. Horav Shlomo Miller’s Shlit”a opinion is that if you are kovea seudoh, meaning that mezonos are the main part of what is being served, as is often the case in a kiddush or a siyum such as erev pesach, even if you did not wash hands, it is considered a seudas mitzvah. He added that in former generations, that was the norm for many bar mitzvos.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a