Pre-heat oven to 350 degrees F. Line a 12-muffin cup pan with silicone baking cups.
Combine the dry ingredients in a large bowl - the flour, oats, baking powder, baking soda, salt and cinnamon.
Then combine the wet ingredients in another, smaller bowl - the applesauce, egg, milk and maple syrup.
Add the combined wet ingredients into the larger bowl of dry ingredients and stir until almost combined.
Then add the diced apple into the muffin batter and stir a couple more times until combined fully.
Divide muffin batter between 12 muffin cups. It's about ¼ cup of muffin batter for each muffin cup.
Bake in the pre-heated oven for 12 - 15 minutes until an inserted toothpick comes out clean.