Well, I guess oat bran isn't technically primal. But I've been using a tablespoon or two of oat bran to reduce my insulin levels. At least, that is what I've been reading:
Study: High beta-glucan oat bran and oat gum reduce postprandial blood glucose and insulin in subjects with and without type 2 diabetes.
High beta-glucan oat bran and oat gum reduce postp... [Diabet Med. 1994] - PubMed result
I've also been reading that the special kind of 7 molecule sugar in avocados also inhibits the release of insulin, so I've been eating those too.