1) Preheat the oven to 180 degrees C.
2) Line 2 (24 case) mini cupcake pans or 2 regular-size (12 case) muffin pans with paper cupcake liners.
3) Mix the flour, sugar, cocoa, baking soda, and salt together in a large bowl. In a separate bowl, mix the coconut milk, oil, vinegar, vanilla, and espresso powder together, until smooth.
4) Pour the wet mixture into the dry mixture and mix with a fork or small whisk. Divide the batter evenly amongst the prepared cupcake liners. The cups should be filled about 2/3-full. Bake until a cocktail stick inserted in the centre comes out clean, about 20 to 22 minutes for the mini cupcakes and about 25 minutes for the regular-size cupcakes. Cool the cupcakes in the pans for 5 minutes and then transfer to a rack to cool completely.
5) To make the frosting, combine the icing sugar, margarine, and vanilla extract in the bowl of a mixer and beat on a medium-high speed until combined. With the mixer running, add 1 tablespoon of water at a time, until the desired buttercream consistency is reached.
6) Slice off the top 1/3 of each cupcake and spread generously with frosting and sliced strawberries. Place the top of the cupcake back on top and add a little more frosting and sliced strawberries. Dust with icing sugar, if using.