In medium bowl, mix together brown sugar, oatmeal, flour, baking powder, salt, and cinnamon.
In small bowl, mix together vegetable oil, egg white, and milk. Using whisk or stick blender, mix well.
Pour wet mixture into bowl with dry ingredients, and mix until moist. Set aside.
Continue heating and stirring the rhubarb mixture until the rhubarb has softened and the mixture looks like jam. Remove from heat and let cool 10 minutes.
Using #70 disher, dollop batter onto cookie sheet. Using fingers that are lightly dipped in water, form a small hollow well in the middle of each cookie – about ¾” diameter and 1/8” deep.
Using two spoons, add about 1 tsp of rhubarb to the hollow well in each cookie.
Using wet fingers, take about 1 tsp of dough from bowl and form into a flat circle – about the size of a quarter. Place it on top of the rhubarb on each cookie. It’s okay if some of the rhubarb remains exposed.
Bake for 12 minutes at 350 F – or until outer edges start to brown. Remove from oven and let cool 10 minutes.