Preheat oven to 350F and line baking sheets with parchment paper.
In a large mixing bowl combine the flour, cinnamon, baking soda, baking powder and salt and set aside.
In separate mixing bowl, cream together the butter, brown sugar, and granulated sugar. Mix in the eggs one at a time and then the vanilla extract. Add in the dry ingredients and mix together then add in the oats and walnuts.
Using a 2 tbsp cookie scoop, transfer balls of dough to the prepared baking sheet, about 2 inches apart. Bake until golden brown around the edges and the center looks slightly under-baked, about 12-15 minutes. Allow to cool on the baking sheet before transferring to a wire rack to cool completely.