Preheat oven to 375°F. Spray a 12-cup muffin tin with cooking spray, or grease with butter.
In a large bowl, whisk together the flour, oats, baking powder, cinnamon, nutmeg, ginger, and salt.
Using a handheld mixer, mix the butter and brown sugar together until light and fluffy.
Add the egg and mix until combined.
Add half the flour mixture and half the milk. Use a spatula to gently mix until just combined. Repeat with the remaining flour mixture and milk.
Gently fold in the apples.
Divide the batter evenly among the muffin cups. Bake for 20–22 minutes, or until the muffins are light golden brown on the edges and a toothpick comes out clean.
Let cool for 5 minutes, then carefully remove from the muffin tin. Eat while warm or let cool and enjoy later.
Notes
You can use a variety of apples here, including Granny Smith, Honeycrisp, Pink Lady, Golden Delicious, Fuji, and Gala. Choose your favorite apple! Take care not to over mix the batter, which can make the muffins chewy/tough.