For the cupcakes: Preheat the oven to 350 degrees F. Line a cupcake tin with paper liners.
Throw your mashed banana in a blender or just smash it with a fork. Sift the flour, sugar, baking powder, cinnamon, salt and baking soda into a large bowl and mix well. Whisk together the soy milk, oil, vanilla, almond extract and mashed banana in a smaller bowl. Stir or fold the wet ingredients into the dry ingredients (small lumps are fine), and then gently fold in the walnuts. Fill the liners two-thirds full and bake until the tops spring back when lightly touched, 20 to 22 minutes. Cool in the pan on a wire rack for 10 minutes, and then remove the cupcakes from the pan and cool completely before frosting.
For the maple buttercream: Beat together the confectioners' sugar, margarine, vegetable shortening, maple syrup, maple extract and salt with an electric mixer until the frosting is pale and fluffy. Divide the frosting evenly between the cupcakes.