Q. According to Rav Shlomo Miller, if a goy cooks meat… by steam or hot smoke is it bishul akum?

A. Rambam (Maachalos Asuros 17: 17) and Shulchan Aruch (Y.D. 113: 13) rule that food smoked by a Gentile does not constitute bishul akum. Remoh (ibid.) adds that this includes preserved foods, since the prohibition applies only to cooked by fire comestibles. Poskim debate whether steam is also exempt. Darkei Teshuva (Y.D. 113: 16, quotes the opinions of the opinions of the Shem Aryeh and Zer Zahav. Proponents of the lenient view argued that steaming is analogous to smoking and not to cooking, since the food is not directly cooked through means of a fire. Another argument for leniency was that since the steaming of foods was first introduced many centuries after Chazal forbade bishul akum, steaming was not a form of cooking that was included in the original decree. Seridei Eish,(2:138), Yabia Omer (5:Y.D. 9) and Mishne Halachos (2: 2: 17) also maintain that steaming is not included within the parameters of the Bishul Akum decree. Other Poskim differentiate between food cooked directly by steam in a steam chamber or if cooked in a pressured container when already canned, using superheated steam. In the last case after all the food is being cooked in the heated liquid inside the can and should be prohibited. (Teshuvos Vehanhagos Y.D 382).
The above is essential in understanding the debate whether canned tuna, salmon, sardines etc. are included in the bishul akum gezeira, although there are other mitigating factors involved. Such as the radically new production methods and equipment completely different from the normal household cooking utensils, that did not exist in the days of Chazal and should therefore not be included in the prohibition. (Minchas Yitzchok (3: 26: 6). Additionally, Horav Moshe Feinstein, zt“l is quoted (Mesorah,Vol.1.) as ruling that there is no prohibition of bishul akum if the non-Jewish cook is unknown to the consumer, since eating this factory prepared food item would not lead to any socialization and eventual intermarriage.
Horav Shlomo Miller’s Shlit’a opinion is that one can be lenient in using smoke as a source of heat for cooking with it. However in regards to steam one should be stringent when possible. In need you may rely on the Poskim that are lenient.

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