If one ate mezonos or fruits for the third Shabbos meal or melava malka (whether due to being lazy, or not having an appetite for bread, or being unable to eat bread due to not feeling well r”l), and later it became possible for one to eat bread, should one do so? Or do we say that since the mitzvah was already fulfilled, there is no point in doing it over in a more ideal way?
If someone ate the mezonos or fruits for the third Shabbos meal or Melava Malka, if he has the opportunity to eat it properly they should do so, and we don’t say that the mitzvah was already fulfilled.
There is controversy if a person has the opportunity to do a mitzvah now, but only in simple way, (i.e. he has a kosher esrog, but it isn’t mehudar) or if he waits he can to it more properly (he’ll have a better mehudar esrog later), if he should wait because if he does the mitzvah now he already did it. However here it is firstly after the fact, and secondly according to many rishonim he hasn’t fulfilled his obligation to eat shalosh seudos if he didn’t eat bread, therefore he should definitely eat bread if he can. The same applies for melava malka.
Moadim Uzamanim 2-118, M”B 291- 22, 23, Levush siman 300,