Heat the oven to 350ºF. Grease a 12-cup muffin tin and set aside.
In a small bowl, whisk together milk, maple syrup and coconut oil. Whisk in the egg. Add the diced mango and mash slightly.
Add the dry ingredients directly into the bowl with the wet and fold gently just until combined
Fill each muffin cup ¾ of the way.
Top each muffin with a sprinkle of sugar in the raw.
Bake on the center rack for 20-24 minutes until the center springs back when touched lightly or when a cake tester inserted into the center comes out clean.
Cool in the muffin tin for 2 - 3 minutes, then transfer to a wire rack and cool completely or they will not set well and fall apart.