Gather the ingredients.
Preheat the oven to 325 F.
Stir together the oats, flour, cinnamon, cloves, allspice, baking powder, and salt in a large bowl.
In a measuring cup, whisk together the maple syrup, egg, melted butter, and vanilla extract. Stir in the peeled and chopped apple.
Slowly mix the wet ingredients into the dry ingredients until they are totally incorporated and the dry ingredients are completely moistened.
Cover and let the dough chill in the refrigerator for about 20 minutes.
Line a baking sheet with parchment paper. Scoop tablespoon amounts of dough onto the parchment paper. Flatten each round ball slightly.
Bake for about 12 minutes.
While the cookies are baking, whisk together the icing ingredients.
Let the breakfast cookies cool on a wire rack and then drizzle them with the icing. Serve the breakfast cookies immediately or place in an airtight container and keep for a few days.
