Preheat the oven to 350 degrees and grease a 9-inch square baking pan.
In a large bowl, stir together the flour, oats, brown sugar, cinnamon, and salt with a fork.
Cut the butter into cubes and add it to the bowl. Use a pastry blender to cut the butter cubes into the dry ingredients. The mixture is mixed enough when the butter is in tiny bits, evenly distributed throughout the mixture. It will look a bit like cornmeal when you have mixed it correctly.
Measure out 1½ cups of the dry mixture. Dump it out in the bottom of your prepared pan and use your fingers or the bottom of the measuring cup to press it firmly into the pan and about an inch up the sides.
Use a spoon to drop the cranberry sauce on top of the bottom crust in large tablespoon-sized globs. Spread this around gently with the back of your spoon until it is in an even layer. Be gentle because you do not want to destroy your bottom crust.
Sprinkle the rest of the dry mixture over the top of the cranberry sauce in an even layer. Top it with the chopped nuts, evenly distributing them over the dry mixture.
Bake the bars in the preheated oven for about an hour. The top crust should be golden brown, and the nuts should be fragrant and toasted.
Let the bars cool completely for about 2 hours before attempting to cut them.
Cut the bars into 12 squares and serve them.