Combine sugar, white rice flour, and oil in a small bowl and whisk with a fork until a sandy mixture forms. Set aside.
Preheat oven to 425 °Fand grease a 12-muffin pan.
In a medium bowl, combine dry ingredients (white rice flour, sugar, baking powder, and salt). Add lemon zest. Gently mix in frozen blueberries, ensuring the berries are thoroughly coated in the dry mixture.
In another bowl, combine wet ingredients (milk, eggs, oil, extract, lemon juice) and whisk until well-incorporated.
Add the dry ingredients to the wet and mix gently with a silicone spatula until just combined. Scrape the sides and bottom to ensure full incorporation.
Portion the mixture between the 12 muffin cups, filling about ⅔ of each cup. Top with streusel.
Bake the muffins at 425 °F for about 15 minutes. Use an internal thermometer at this time to ensure muffin temp has reached about 200 °F. Remove from oven.
Allow to cool in the pan for about 5 minutes before removing. Enjoy with a cup of coffee!