In order to stabilize certain enzymes in oats that cause a bitter taste, Oats are heated, the oats contain moisture that steams from the heat.
Of course it's a Pesach oat matzo issue.
The ones that are involved in making pesach oat matzos don't want to talk about the process of the steaming.
[From a University professor-"Before flaking processed oats are steamed. The heat and moisture improves flaking but also inactivates enzymes that can cause rancidity and other off flavors. Steaming is for 12-15 minutes and the oat temp rises from ambient to 210 – 220 F". ]There is another issue re: bishul akum. After the oats are steamed, they are techinically edible albeit not al shulchan milochim, so that may be a bishul akum issue.
The Minchas Yitzchok address the issues in chelek gimel, siman 72.