Preheat the oven to 350 degrees . Grease a 9-inch square baking pan.
In a microwavable bowl, combine the cranberry sauce and sugar. microwave at high power for 1 minute. Stir, then heat in 30-second intervals until the sugar dissolves and the mixture is spreadable.
In a medium bowl, combine the flour, oats, brown sugar and salt. Using your fingers, rub the butter into the dry ingredients until the streusel is crumbly. Stir in the walnuts.
Firmly press 2 cups of the streusel into the baking pan. Spread the cranberry mixture over the crust. Sprinkle with the remaining streusel.
Bake until the top is lightly browned, about 30 minutes. Let cool completely before cutting into squares.