Preheat oven to 350°. Line cookie sheets with parchment paper.
In a large bowl, whisk together flour, baking powder, baking soda, cinnamon, and salt until well-mixed.
In a stand mixer (or large bowl if using traditional mixer), cream together butter, sugar, and brown sugar approximately 3 minutes, until light and fluffy.
Add eggs one at a time, beating well after each addition. Scrape down bowl.
Beat in vanilla. Scrape down bowl.
On low speed, add flour mixture gradually, approximately 1/3 cup at a time. Beat until just blended (don't over-mix!).
Stir in oats, raisins, and pecans.
Drop large tablespoons full of dough onto parchment-lined cookie sheets. Make sure you leave room between cookies for them to expand.
Bake- one sheet at a time- for 10 to 12 minutes. Pull out the cookies before they look entirely done (they will harden as they cool).
Slide parchment paper onto cooling rack. Allow to cool for 5 minutes. Transfer cookies from parchment paper onto another cooling rack and allow to cool.