In a small saucepan over medium high heat, combine the cranberries, white sugar and orange zest. Bring to a boil, then reduce heat and cook until the mixture has reduced to about 1 cup.
Preheat oven to 350 degrees F (175 degrees C). Grease a 9x9 inch baking pan, line with foil, then grease the foil.
In a medium bowl, stir together the flour, oats, brown sugar, baking powder and salt. Cut in the butter using your hands or a pastry blender until the mixture resembles coarse crumbs. Press half of this mixture firmly into the prepared pan. Spread the cranberry sauce evenly over the base, then crumble the remaining oat mixture over the top.
Bake for 10 to 15 minutes in the preheated oven, until the top is golden brown. Cool completely before cutting into bars.
