chia works as well in some applications.
i agree that the flour/water mixtures of whatever stripe you wish to name won't work for a cookie, which requires driving more moisture out to get the desired effect. with all due respect to the op, this is something of a fool's errand unless you really get into some of the more novel technical ingredients
the closest to a low-ish calorie chocolate cookie that you can easily make imo are something like the flourless fudge cookies. here's a king arthur version of this recipe:
https://www.kingarthurbaking.com/recipes/flourless-fudge-cookies-recipe
if you were to replace the sugar with a combination of non-nutritive or at least low-calorie sugars, it works pretty well. that in and of itself requires some experimentation, though.
