Engineers and Infiltrators have access to this ability. In addition, so does Mordin.
Whenever you encounter an enemy with armor, you should try shooting them a bit to lower said armor, especially on "Insanity", before using Incinerate. This is because the power needs to remove the entirety of what's left of the armor for it to count.
Credit to Fauved for their
guide. Additional information sourced from the
wiki.