Preheat oven to 200 C / Gas 6. Grease a 12-hole muffin tin or line with paper cases.
Stir wholemeal flour, oats, sugar, baking powder, bicarbonate of soda and chocolate chips together in a bowl. Make a well in the centre. Whisk eggs in a separate bowl until frothy; mix applesauce, skimmed milk and banana into eggs. Pour moist ingredients into dry ingredients; stir just to moisten. Batter will be lumpy. Fill prepared muffinholes about 3/4 full.
Bake in the preheated oven until a skewer inserted into the centre of several muffins comes out clean, 16 to 18 minutes. Cool in tin for 5 minutes before removing to finish cooling on wire racks.