What do you mean by fermented. I have made itin the past using sprouted grains. You could make it with rejuvelac (fremented liquid make from sprouted wheat berries). Are mix it with yogurt which is fermented (I think). Why are you wanter fermented porridage? I think spouted cereal would be just as good. You could always take a probiotic with it.
If you find a recipe, please post for everyone. I would to try it out.