Preheat the oven to 180C. Spray the donut pan with cooking spray and set aside. Sift the flour into a large bowl. Then add sugar, baking powder, cinnamon, and salt and whist together. Add the soy milk, vanilla extract, mashed bananas, and melted margarine and stir everything to combine. Transfer the donut batter into a piping bag and pipe it evenly into the prepared donut tray. Alternatively, you can do this using a teaspoon. Bake the donuts for 20 minutes, until the top is lightly browned and toothpick comes out clean. Once done baking, remove from the oven and let cool for 10 minutes. Remove donuts from the tray and let cool completely on a cooling rack. Melt the white chocolate. Dip the top of each donut in the chocolate and sprinkle with the pistachios.