In a large bowl, whisk together the rolled oats, all-purpose flour, baking soda, ground cinnamon, salt, light brown sugar, and granulated sugar until well combined.
Stir in the semisweet chocolate chips and chopped walnuts evenly into the dry mixture.
If preparing the cookie jar as a gift or for storage, layer the dry ingredients neatly in a clean, airtight jar and seal until ready to bake.
To bake cookies from the jar mix, preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a separate medium bowl, cream the softened unsalted butter with the egg and vanilla extract until smooth and creamy.
Gradually add the dry mixture from the jar into the wet ingredients, mixing until just combined to form cookie dough.
Drop rounded tablespoons of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake for 9 to 11 minutes or until the edges are golden brown and the centers are set.
Remove the cookies from the oven and allow them to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.