Preheat oven to 350 degrees (F). Generously grease a doughnut pan; set aside.
In a small bowl whisk together flour, baking powder and salt; set aside.
In a large bowl combine the granulated sugar and lime zest; mix together with your fingers until zest is evenly distributed in the sugar. Add in the melted coconut oil and, using a whisk, mix until combined. Beat in the egg, then stir in coconut milk.
Add in the dry ingredients and gently fold the mixture together using a rubber spatula, stirring only until mixture is evenly combined.
Divide the thick batter evenly among the molds of your prepared pan, filling each mold up 2/3 of the way. Bake for 10-11 minutes, or until firm and lightly golden on the tops.
Remove pan from oven and allow doughnuts to cool for at least 10 minutes in the tray before transferring to a cooling wrack to cool completely.
Once cool, dip each doughnut in glaze and serve! The glaze does take a few minutes to set, so you may want to wait about 5 minutes after glazing to dig in... but it's hard!
For the Key Lime Glaze:
In a wide, shallow dish combine juice and sugar, and whisk to combine. If the glaze appears too thick, add a little more lime juice until desired consistency is achieved; if glaze appears too thin, add a little more confectioners' sugar until desired consistency is achieved. Carefully dip cooled doughnuts in the glaze, and let rest for 5 minutes - if you can wait - before serving. If you'd like your donuts to look exactly like mine do in the photos, top each glazed donut toasted coconut and extra lime zest.