Preheat the oven to 300 degrees F. Spray a large baking sheet with cooking spray.
In a medium bowl combine the oats, nuts, maple syrup, salt, cinnamon and the raisins, if using. Spread the mixture onto the baking sheet and bake until golden brown, stirring occasionally, about 30 minutes. Transfer the sheet to a cooling rack and let cool completely. Store in the refrigerator in an airtight container.