Combine the oats, cranberries, walnuts, brown sugar, and cinnamon in a bowl. Stir until evenly mixed. Store mixture in an air-tight container in a cool dry place until ready to eat.
To prepare the muesli, combine 1/2 cup muesli with 1/2 cup of cold milk. Let soak for 5 minutes, or up to four days in the refrigerator.