SLOW Carb carb source for DIY recipe?

Hi guys,

I’m not a breakfast person and would love to go liquid at least for thi meal, potentially more.
Yet I’m mostly eating SLOW carb (note: not low carb).

Here’s some reference for orientation.

Is there any slow carb carb source in powder form that could be mixed into a liquid meal replacement instead of the usual oats or corn starch etc.?
Coconut flour? Flaxseed powder? other? A mix of different ones?
Lentil flour is not an option as far as I know as it can’t be digested uncooked.

Oat flour seems popular and has a low GI.

Isomaltulose is a sugar with a very low GI of around 32.

oatmeal is not allowed on that diet - sadly!

Never heard of that, interesting!

Is there any carb powder from legumes or green veggies?

How about flaxseed, chia or coconot flour? If I’d want to replace oatmeal with one of thoflaxseed or chia, coconot floure or a mix - how to calculate?