Preheat oven to 350F and line a muffin tin with liners.
Whisk the pumpkin puree, coconut sugar, milk, eggs, butter or oil, and maple syrup together in a large mixing bowl until smooth.
Add the flour, oats, baking powder, cinnamon, and salt to the mixing bowl and stir to incorporate into the wet ingredients. Fold in the diced apples.
Evenly distribute the batter to fill the 12 muffin liners, then bake until browned and a toothpick comes out clean, 26 to 30 minutes.
Let cool completely before enjoying (this is important as they will stick to the muffin liners if not fully cooled). Store in an airtight container on the counter for up to 4 days.
