Preheat oven to 350°.
In a medium bowl beat brown sugar, mayo, egg, and vanilla for about 2 minutes. (You can use a hand-held mixer or stand mixer, but grandma recommends doing it by hand.) Set aside.
In a large bowl, combine oats, flour, cinnamon, and baking soda.
Slowly add the mayo mixture to the oat mixture and stir by hand until just combined.
Stir in chocolate chips. (I save a few to place on top before baking)
On prepared baking sheets, drop dough by level tablespoonfuls, 3-inches apart. (they will spread some)
Bake 8-10 minutes or until golden.
Cool cookies on a wire rack.