For obvious reasons, microwave cooking is not discussed in the Talmud or Shulchan Aruch. Nonetheless, some contemporary poskim equate microwave cooking to the cooking process of smoking. The Shulchan Oruch (Yoreh Deah 113:13) rules that food that is smoked by a Gentile is not treated as bishul akum because the Rabbis did not prohibit unusual cooking methods. Since microwave cooking is a new innovation, it is treated as unconventional, and bishul akum would not apply. Other contemporary poskim argue that today, microwaves have become a standard mode of cooking and therefore bishul akum is a concern. We therefore recommend that you consult your local Rabbi or community kashrus agency.