Preheat the oven to 350 degrees F and spray a donut pan with non-stick spray.
Whisk the flour, cocoa powder, sugar, baking powder, salt in a large bowl. Pour the soy milk, melted vegan butter and vanilla into the bowl with the dry ingredients. Mix well with a large wooden spoon to combine.
Spoon the batter into the donut pan, filling about 3/4 of the way full.
Bake for 10-12 minutes or until the donuts look set on top. Let cool for two or three minutes in the pan, then carefully transfer to a wire rack with a large piece of parchment paper beneath it (to help with the mess). Let the donuts cool completely before dipping in glaze.
Make the glaze: In a medium sized bowl, add powdered sugar, soy milk and vanilla. Stir with a spoon until a smooth glaze is formed.
Once the donuts have cooled completely, dip the entire donut into the glaze carefully, then place back on the rack over parchment paper to set. It will take 30 minutes or so for the icing to harden, but of course you can eat them right away if desired!