Preheat an oven to 160 degrees C. Grease and flour two loaf tins.
Whisk the plain flour, wholemeal flour, salt, bicarb soda, baking powder, cinnamon and nutmeg together in a bowl. Beat the bananas, eggs, vegetable oil, apple sauce, brown sugar, white sugar and vanilla together in a separate large bowl. Stir the flour mixture into the wet mixture. Fold the zucchini, walnuts, and coconut into the batter until evenly combined. Pour into the prepared pans.
Bake in the preheated oven until a skewer inserted into the centre comes out clean, 40 to 50 minutes. Cool in the pans for 25 minutes before removing to cool completely on a wire rack.