Preheat oven to 350°F. Mix together flour, flax, oats, baking soda, cinnamon and salt.
With an electric mixer, beat together butter and brown sugar for one minute, until the mixture is smooth. Add the egg and vanilla. Scrape down sides, and continue to blend until incorporated. Add flour mixture a little at a time until incorporated. Stir in chocolate chips.
Spray three large cookie sheets with cooking spray, and mound 12 rounded tablespoonfuls of batter on each sheet. Bake for 8-10 minutes, swapping sheets half way through, until golden. Let cool slightly, for 5 minutes, and slide cookies onto a cooling rack.