Q. When traveling we realized that for the Shabbos day meal we only had one challa. Can one in such a case use a cake or doughnut as the adjoining lechem mishna?
A. Horav Shlomo Miller’s Shlit’a opinion is that if one eats a proper amount of kevias seuda of mezonos he complies with lechem mishna (See similar opinions in Shaarei Teshuva 274: 2, Kaf Hachaim ibid. 6, Ketzos Hashulchan 82: 5, etc.). In this case placing that amount of mezonos next to the challa can be regarded as lechem mishna.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a