Preheat oven to 350°F Grease 8 muffin cups in a baking tin.
In a medium bowl, whisk together flour, cocoa, baking soda, baking powder and salt.
In a small bowl, whisk together maple syrup, soy milk and vegetable oil. Pour wet ingredients into flour mixture and stir until smooth, adding walnuts at the last minute. Do not over mix, but try not to have any pockets of dry ingredients left in the batter. Spoon into prepared muffin tins, filling each 2/3 full. Garnish each muffin with a walnut half.
Bake for 18-20 minutes, until the top springs back when lightly pressed.
Let cool slightly before serving. Allow to cool completely on a wire rack, before storing well wrapped or in an airtight container.