In food processor, combine oats, flour, sugar, baking powder, baking soda, salt, and nutmeg; pulse to blend. Add butter; pulse until coarse crumbs form.
In cup, beat buttermilk and egg. With processor running, add egg mixture and pulse until a dough forms.
Scoop dough by 1/4 cups onto cookie sheet. Flatten each mound into a 2 1/2-inch round. Sprinkle with cinnamon-sugar. Bake 15 to 17 minutes or until golden on bottoms.