Melt the coconut oil, and set aside to cool slightly.
Combine the milk and lemon juice, and set aside.
Heat the oven to 340 degrees.
In a large bowl, combine the flour, baking powder, baking soda, and salt.
In a medium bowl, combine the milk, sugar, coconut oil, and vanilla.
Slowly pour the wet into the dry, stirring as you pour.
Mash the bananas, and stir them into the mixture.
Pour the batter into cupcake tins (lined with liners) and bake at 340 for 30 minutes, until a toothpick comes out clean.
Cool completely, for at least an hour.