Preheat oven to 375 F. In a medium mixing bowl, mix bananas, coconut sugar and eggs with a mixer on medium speed until well combined. It's okay if there are some banana chunks.
Add coconut flour, oat flour, coconut oil, vanilla extract, baking powder and salt to the mixing bowl and mix well (on low speed, if using the mixer).
Fold in dark chocolate chunks. If you don't like chocolate or want to avoid using chocolate, you can just omit it, or add instead nuts of your choice (like chopped walnuts or pecans). It will turn out great that way too!
Spread mixture in a 8 x 8 baking dish and bake in a preheated 375 F oven for 25 minutes.
Place the baking dish on a cooling rack and let brownies stand for 5 minutes before cutting.
Melt chocolate chips/chunks in a glass bowl over pan with boiling water. Drizzle some melted chocolate on top of already cut brownies and enjoy! It is hard to eat only one brownie. :)