Line 10 muffin cups with liners or lightly grease them.
Whisk brown rice flour, corn starch, potato starch, baking powder, baking soda, salt, and poppy seeds in a medium bowl.
Beat the eggs, oil, sugar, and lemon zest in a large bowl. Add the milk and the lemon juice and mix. Add the flour mixture and mix until incorporated well.
Pour the mixture into the prepared pans. Fill the muffins 3/4 full, dividing as evenly as possible.
Bake for 20 minutes or until a toothpick inserted into the center comes out clean.
Let cool before removing.
For the lemon icing
Squeeze half a lemon.
In a medium bowl mix sugar with two tablespoons of lemon juice. Mix and add more tablespoons of juice, little by little, and integrate it until you get the desired consistency. The frosting should not be too runny.
When the muffins are completely cold, spread the icing on the top. Finish with poppy seed.
Notes
Store the muffins in an air-tight container at room temperature for up to 3 days or in the refrigerator for up to 5 days.