Preheat oven to 375°F (190°C). Line a 6-cup muffin tin with paper liners.
In a small bowl, combine 2 tablespoons sugar and 1/2 teaspoon lemon zest. Rub the zest into the sugar with your fingers to release the oils.
Add 1/3 cup gluten-free flour and 2 tablespoons melted vegan butter. Mix until combined. Set streusel aside.
In a large bowl, whisk together 1 cup + 2 tablespoons gluten-free flour, 1 1/4 teaspoons baking powder, and 1/4 teaspoon salt.
In a separate bowl, whisk the egg until frothy. Add 3 tablespoons olive oil, 6 tablespoons non-dairy milk (or regular milk), and 2 tablespoons lemon juice. Stir to combine.
Add the wet ingredients to the dry ingredients. Gently fold about 10 times until just combined.
Gently fold in 3/4 cup fresh blueberries, saving some for topping.
Divide the batter into the prepared muffin cups, filling each almost to the top.
Sprinkle remaining blueberries and the streusel topping over each muffin.
Bake for 20-25 minutes, until golden and a toothpick comes out clean.
Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.