Preheat the oven to 180°C. Spray a 23 x 13 cm loaf tin with cooking spray. Toast the oats in a small baking dish, stirring occasionally, for 10 minutes or until lightly browned. At the same time, toast the pecans in another small baking dish for 7 minutes or until fragrant and lightly browned. When the nuts are cool enough to handle, chop coarsely.
Mash the bananas in a large bowl until not quite smooth. Add the buttermilk, oil, egg whites, vanilla essence and both sugars, and mix until well blended; put aside.
Combine the flour, baking powder, bicarbonate of soda and and a pinch of salt in a small bowl. Fold the dry ingredients into the banana mixture along with the oats and pecans until just combined. Do not overmix. Spoon the batter into the prepared tin, smoothing the top. Bake for 1 hour and 25 minutes or until a skewer inserted in the centre comes out clean. Cool in the tin on a rack for 10 minutes. Turn out of the tin onto the rack to cool completely.