Lechem Mishneh
ANSWER: Matzos, bagels, pitas, or any other type of bread, may be used for lechem mishneh.
It is preferable to eat only pas Yisrael on Shabbos. One who does so, may use bread that is not pas Yisroel for the second loaf. Pri Migadim explains that if one only has loaves that are pas akum, they may be eaten on Shabbos, even though one is normally stringent. (Pri Megadim M.Z. 274:2).
One may borrow a challah (or any other bread) from a neighbor to use as lechem mishneh, even though it must be returned and cannot be eaten (Shemiras Shabbos K’hilchasa 55:13).
Rivevos Efraim (1:202) writes that one may even use dairy bread (which was made according to halacha, either made in a small batch or with a unique shape) as the second loaf for a meat meal, even though it may not be eaten at the meat meal.
If one does not have a second loaf, hamotzi should be recited on a single challah.
____________________________________________________
The Gerald & Karin Feldhamer OU Kosher Halacha Yomis is dedicated to the memory of Rav Yisroel Belsky, zt"l, who served as halachic consultant for OU Kosher for more than 28 years; many of the responses in Halacha Yomis are based on the rulings of Rabbi Belsky. Subscribe to the Halacha Yomis daily email here.