Preheat oven to 350°. In a large bowl, whisk flour, baking powder, baking soda and salt. In a small bowl, whisk coconut milk, sugar, oil, vinegar and vanilla. Stir into dry ingredients just until moistened.
Fill paper-lined muffin cups half full. Bake until a toothpick inserted in the center comes out clean, 15-20 minutes. Cool 10 minutes before removing from pans to wire racks to cool completely.
For frosting, in a large bowl, beat margarine until light and fluffy. Beat inconfectioners’ sugar, milk and vanilla. Frost cupcakes.