Place small amount of oats in blender container; process until powdered. Repeat until all oats are powdered. Combine powered oats, flour, baking powder, baking soda, and salt; mix well. In large bowl, beat butter and sugars with electric mixer until light and fluffy. Blend in eggs and vanilla. Add dry ingredients to sugar mixture; mix well. Stir in chocolate and walnuts. Chill at least 1 hour. Preheat oven to 375°F. Dip cookie dough with cookie scoop; place 2 inches apart on ungreased cookie sheet. Bake 10-12 minutes or until lightly browned. Remove cookies to wire rack to cool.
Freeze Ahead Directions: Prepare cookie dough as directed above. Using cookie scoop, drop balls of dough, close together, onto ungreased cookie sheet. Freeze. Place frozen dough in airtight container. When ready to bake, preheat oven to 375°F. Place frozen cookie dough, 2 inches apart, on ungreased cookie sheet. Bake 15-20 minutes or until lightly browned.