Gemahlene Leinsamen und Wasser in eine kleine Schüssel geben, um ein Leinsamen-Ei herzustellen. Beiseitestellen, damit es quillt. Den Ofen auf 170 Grad vorheizen.
Combine peanut butter, apple sauce, date syrup and flax egg in a large mixing bowl. Add GF oat flour, cocoa, baking powder and salt. Whisk to combine, batter will be thick. If you want to add chocolate this is the right time; reserve a few chunks to scatter on the surface of the brownies.
Line a 20x20cm cake tin with parchment paper, leaving the ends loose for easy lift once brownies are baked. Transfer the batter to prepared tin and bake for 25-30 minutes. The surface of the brownies will be solid but the center should still have some give to it.
Cool the brownies completely (at least 3 hours) before slicing and serving with a dollop of coconut yogurt. Leftovers can be stored in an airtight container for up to three days.