Preheat oven to 350 degrees. Spray a 9×9 inch baking dish with non-stick cooking spray. In a small bowl, combine the flour, oats, and brown sugar. Stir in butter until butter and flour/oats are combined. Set aside 2/3 cup of the mixture for the topping. To form the bottom crust, press the remainder of the mixture into prepared baking dish.
Meanwhile, to make the filling, combine the cranberries, mandarin oranges, jello mix, and sweetener in a medium saucepan. Cook and stir over medium high heat for 20-25 minutes, or until berries have popped, and mixture is beginning to thicken.
Pour filling over crust, and sprinkle remainder of the oat mixture over the top of the cranberry filling. Bake for 35 minutes, turn oven off, and allow bars to sit in the oven for an additional 15 minutes, (this allows cranberry filling to set).
Remove bars from the oven and allow to cool the rest of the way. Cut bars into 9 even squares. Enjoy!