Preheat oven to 350 degrees F. Prepare a baking sheet by lining it with parchment or a Silpat pad.
Peel, core, and dice the apple into small pieces. Place into a small bowl and toss with the lemon juice; set aside.
In the bowl of a mixer fitted with the paddle attachment, cream the butter and sugars until soft and light.
Add the egg and vanilla. Beat until well combined.
In a medium bowl, whisk together the flour, oats, baking powder, baking soda, cinnamon, nutmeg, and salt.
Pour into butter mixture and beat until just blended. Mix in the apple.
Bake for 10-13 minutes or until desired doneness. Cool for 5 minutes on baking sheet before transferring to wire rack to cool completely.
Compliments of 365 Days of Baking and More