Preheat the oven to 350 degrees.
Whisk the dry ingredients (oat flour, cocoa, carob (if using), salt, baking soda, ground chia seeds, and sugar).
Mix the wet ingredients in a separate bowl (liquid sweetener, vanilla, prune puree, oil, and water).
Stir all of the ingredients together until thoroughly combined and there are no lumps. Stir in the chopped chocolate last (or sprinkle it atop the batter once you've poured it into the dish).
Oil an 8 x 8 baking dish, and pour the batter into the dish.
Bake the brownies for 20-23 minutes (they should feel fairly firm if you press lightly on the top of them).
Allow them to cool (they will firm up more during this time as well).