Mix together flour, baking soda, and cinnamon.
Beat together butter, brown sugar, and granulated sugar at medium speed
until light and fluffy. Beat in egg and vanilla.
At low speed, beat in flour mixture until blended. Fold in oats and
chocolate chips. Cover with plastic wrap; chill for 1 hour.
Preheat oven to 350° F. Grease 2 baking sheets.
Shape dough into 1-inch balls. Place cookies, 2 inches apart, on prepared
baking sheets. Flatten each cookie slightly.
Bake cookies until lightly browned around edges, 10 - 12 minutes. Transfer
baking sheets to wire racks to cool slightly. transfer cookies to racks
to cool completely.
Hint: make dough ahead of time and freeze it. Later, use defrosted
dough to make homemade cookies in minutes.