Prepare the Dough
Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper or a silicone mat.
In a large mixing bowl, combine oats, flour, baking powder, cinnamon, nutmeg, and salt. Mix well.
In a medium bowl, whisk together melted coconut oil (or butter), maple syrup (or honey), and vanilla extract until smooth.
Combine Wet and Dry Ingredients
Pour the wet ingredients into the dry ingredients and stir until just combined. Fold in the diced apples.
Shape the Cookies
Scoop 1 1/2 tablespoons of dough per cookie onto the prepared baking sheet. Flatten slightly with the back of a spoon or your fingers.
Bake
Bake in the preheated oven for 12–15 minutes, or until the edges are lightly golden. Remove from the oven and let cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.