In a medium mixing bowl, whisk together the oats, whole wheat pastry flour, baking powder, cinnamon, salt, and nutmeg.
In a small, microwave-safe bowl melt the butter. Let cool for a few minutes, then whisk in the vanilla extract and egg. Once smooth, whisk in the honey until well combined.
Make a well in the center of the dry ingredients, then pour in the wet ingredients. With a wooden spoon or rubber spatula, stir just until the ingredients are combined and the flour disappears (do not over mix). Fold in the diced apples.
Cover the bowl with plastic wrap and place in the refrigerator for 30 minutes to allow the dough to firm slightly.
When ready to bake, preheat the oven to 325 degrees F. Line a large baking sheet with parchment paper or a silpat mat. With a cookie scoop or spoon, scoop the dough by generous tablespoons, then shape into slightly flattened balls. Arrange the cookies 2-inches apart on the prepared baking sheet.
Bake for 10-12 minutes, just until the edges of the cookies appear dry and barely begin to brown. Let rest on the pan for 2 minutes, then transfer to a wire rack to cool completely.
While the cookies cool, prepare the glaze. In a small bowl, whisk together the powdered sugar, vanilla, and 1 teaspoon of milk. Continue adding milk, 1 teaspoon at a time, until desired consistency is reached. Drizzle over the cookies, let set for a few minutes, then enjoy!
Notes
TO STORE: Store cookies in an airtight container at room temperature for up to 3 days.
TO FREEZE: Bake cookies may be wrapped tightly in plastic and kept in the freezer for up to 2 months.