Preheat your oven to 375° and line a 12-count muffin tin.
In a medium mixing bowl, mix together the flour, protein powder, baking powder, and baking soda. Set aside.
In a separate bowl, stir together the granulated sugar and lemon zest.
Whisk in the plain Greek yogurt, oil, milk, eggs, vanilla extract and lemon extract until no lumps remain.
Add the dry ingredients and stir until just combined.
Divide the batter evenly between 12 muffins, then bake for 18-20 minutes or until a toothpick inserted in the center comes out clean. Allow to cool.
While the muffins are cooling, make the drizzle. Whisk together the powdered sugar and lemon juice until smooth. Drizzle it over the cooled muffins, then serve!