Preheat oven to 350 degrees Fahrenheit. Line a 13x9-inch baking dish with parchment paper leaving a 2-inch overhang on each side (for lifting the bars out) or lightly grease with cooking spray.

For the crust and crumb topping: In a large bowl, mix together the butter, brown sugar, oats, flour, baking powder, salt, and cinnamon. Mix until there are no butter chunks and the mixture is starting to clump together. (Can mix with a stand mixer and paddle attachment or with hands.) Set aside.

For the cranberry filling: Rinse and drain cranberries. In a large bowl add the cranberries, sugar, cornstarch, orange zest and juice. Stir to combine.

Press 2/3 of the crumble mixture on the bottom of the prepared pan. Evenly distribute the cranberry mixture over the crust. Sprinkle the remaining crumble over the cranberries. (Press crumbs together for larger clumps, or pat gently after sprinkling on top.)

Bake at 350˚F for 45-50 minutes or until the crust browns and the filling bubbles in the center, not just the sides. Cover with foil if crust is browning faster than the center bubbles. For best results, CHILL in the refrigerator for 1-2 hours before icing and serving.

For the orange icing: Whisk together the powdered sugar, orange zest, and orange juice to the desired consistency. May place icing in a zip-top bag, make a small cut in one corner and drizzle over the cool bars. Or simply drizzle the icing over the top with a spoon. Use parchment paper to lift bars out of pan. Cut and serve.