Preheat your oven to 375 degrees F and line your baking sheet with parchment paper.
In a large bowl, cream together the light brown sugar and softened butter until smooth. Add the vanilla extract and egg, continuing to beat until well incorporated.
Gradually mix in the all-purpose flour, cinnamon, salt, baking soda, and baking powder until a dough forms.
Fold in the finely diced rhubarb until evenly distributed throughout the dough.
Using a cookie scoop, form 1-inch balls of dough and place them on the prepared baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 12-14 minutes, or until the cookies are just set and slightly golden.
Allow the cookies to cool on the baking sheet for 2 minutes before transferring them to a wire rack to cool completely.
