Break up the whole eggs with a fork, then mix with the mashed banana, oil and milk until all the wet ingredients are well combined. In a separate, large bowl tip in the remaining sugar, flour and pecans, and briefly stir with the cinnamon and baking powder. Whisk the egg whites until just stiff. To combine, tip the oily banana mixture into the bowl of dry ingredients and quickly stir in until you have a smooth, lump-free mix. Finally using a large metal spoon or spatula gently fold in the egg whites, then carefully pour the mixture into the prepared tin. Scatter over the crumble topping and bake for 1 hr, until a skewer stuck in to the middle comes out clean. Check the cake with 15 mins to go, if the surface is browning too quickly cover with another piece of baking parchment.