To a large mixing bowl add the melted butter, mashed bananas, sugar, egg, vanilla, cinnamon, nutmeg, baking powder, baking soda and salt and whisk until thoroughly blended, about 1 minute. Alternate adding the flour and water in two batches, starting with the flour and ending with the water. Fold in the chocolate chips and set the bowl aside and let the batter rest while you heat the oven (ideally let the batter rest for 10 to 20 minutes; this is optional!).