Preheat the oven to 350 degrees Fahrenheit. Grease a muffin tin with nonstick cooking spray and set aside.
In a large mixing bowl stir together sugar and canola oil.
Add the egg and mix until incorporated.
Add the gluten free all purpose flour, baking powder, baking soda, and kosher salt to the mixing bowl. Stir until a smooth and thick batter forms.
Stir in the lemon juice, zest, and milk. Scoop the batter into the muffin tin all the way to the top of the tin. You should get 5 muffins.
Bake for 21 to 22 minutes or until a toothpick comes out clean.
While the muffins cool make the glaze. Stir together the powdered sugar, 1 tablespoon of lemon juice, and zest together. If it's too thick, add a little bit more lemon juice.
While the muffins are slightly warm drizzle the glaze over the tops. Enjoy!