Preheat the oven to 350F (177C) and place a rack in the center of the oven. Grease a 8-inch (x-cm) square baking dish and line the bottom of the pan with parchment paper.
In a large bowl, add both sugars, butter, eggs, real vanilla extract, nutmeg and whisk until lighter in color and thick in consistency, about 2 minutes. Add the baking soda, baking powder, sea salt and oat flour, whisking to combine. Then gently fold in the bananas.
Alternate adding the flour and water in two batches, mixing each until just combined. completely. Fold in the chocolate chips and pour into the prepared pan.
Sprinkle with the uncooked oats, sugar and lastly the chocolate chips.
Bake in the center of the oven for 45 to 50 minutes. Set on a rack to cool
Use a gentle hand when stirring the oat flour and bananas into the batter.