Preheat your oven to 350°F (175°C) and grease a doughnut pan.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, salt, and cinnamon.
In another bowl, mix the buttermilk, melted butter, egg, vanilla extract, and lemon zest until well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined.
Gently fold in the blueberries.
Spoon the batter into the prepared doughnut pan, filling each cavity about 2/3 full.
Bake for 10-12 minutes or until a toothpick inserted into the center comes out clean.
Allow the doughnuts to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
For the glaze, whisk together the powdered sugar, lemon juice, and lemon zest in a small bowl until smooth.
Dip the tops of the cooled doughnuts into the glaze and let them set on the wire rack.