In a wide bowl, combine egg whites, maple syrup, baking powder, baking soda, and pinch of salt. Pour apple cider vinegar over the baking powder/soda portion.
Whisk until frothy and combined.
Add vanilla paste and apple sauce. Whisk until totally combined.
Switch to a spatula or spoon. Add flour and oats. Fold into the batter until just-combined.
Add in the banana as the last ingredient. Fold in slowly and do not over mix (or the bananas will change into a gummy-starch).
Spoon batter into prepared cake pans. Bake time: For mini cupcakes, check if baked through at 14 minutes (may need up to 16). For 4" cake pans, check at 24 minutes, may need to bake longer, depending on your home oven. Allow cake to completely cool before topping.