1. Preheat oven to 350°.
2. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking soda, cinnamon, and salt in a bowl, stirring with a whisk.
3. Place butter and sugars in a large bowl; beat with a mixer at medium speed until well blended. Add egg, beating well. Add flour mixture; beat. Stir in oats, chocolate chips, and nuts.
4. Drop dough by 2 level teaspoonfuls onto a baking sheet lined with parchment paper. Bake at 350° for 10 minutes. Remove cookies from pan; cool on wire racks.
Tip: Choose your brand of chocolate chips carefully. Read the label to make sure you select a truly safe gluten-free option.