In a small bowl, combine the oats and buttermilk and stir. Cover and refrigerate overnight.
Preheat the oven to 425°. Prepare a muffin pan by lining with paper muffin liners and spraying each with vegetable spray. Set aside.
In a large bowl, combine the flour, baking powder, baking soda, salt and brown sugar and stir together. Add the oatmeal mixture, melted butter and egg, stirring until well combined. Mix in the pecans, cranberries and orange zest.
Transfer the batter to the prepared muffin tins and bake for 18-20 minutes or until a cake tester comes out clean and the muffins are golden brown. Can be stored in an airtight container for up to 3 days or freeze them for up to 3 months.