Pesachim 39B quotes a Beraisa which says, "The following do not become Chametz: something (i.e. grain) that was already baked (matzo), cooked, or Chalut (scalded, I guess?) in boiling water."
Then the Gemorah asks a question how it could be cooked, since while the water would be heating up the grains (or flour?) would become Chametz, to which it answers that it means something that was baked and cooked.
However, I am not comfortable with the Gemorah's answer. It already said that something baked cannot become Chametz. Something that was baked and something that was baked then boiled have both been baked. So if that's what the Beraisa actually meant, it was redundant (not to mention misleading).
Furthermore, another answer comes to mind which would address the Gemorah's concern about lukewarm water very nicely: Pour the grain or flour into water that is already boiling. Why does the Gemorah not even suggest this answer? That answer seems to fit much more nicely with the Beraisa while addressing the Gemorah's concern just as well.
Note: I am a bit biased, this question jumped out at me from a wish that oatmeal and cream of wheat would be Kosher for Pesach.