re: what is the glutinous substance that comes out of cooked oats that so resembles gluten?
Perhaps some analog of gluten, as the avenin protein of oats is an analog of gliadin. Being sky-hi-gly is not the only problem with oats (for example, 70% of production in the US contains troubling levels of Ochratoxin A).
Oats are commonly cross-contaminated with wheat, but not likely to the extent that gluten is present in amounts useful for texture.
Wheat Free Market Foods sells a GF low carb granola for anyone who doesn't want to make their own.