Preheat oven to 375°. Line cookie sheet with parchment paper.
In large bowl, beat brown sugar, butter, vanilla and egg together with mixer.
Add flour, cinnamon, salt, baking soda and baking powder. Beat well until dough forms.
Add rhubarb and beat again.
Scoop dough into 1 inch balls and place on parchment paper.
Bake cookies for 12-14 minutes or until baked through.
Cool cookies on baking sheet for 2 minutes then move to wire rack to cool completely.