Preheat your oven to 350°F (175°C). Grease a loaf pan.
In a mixing bowl, whisk together the gluten-free flour, baking powder, baking soda, salt, and poppy seeds.
In another bowl, beat the sugar and eggs until light and fluffy. Add the vegetable oil, milk, lemon zest, and lemon juice. Mix well.
Combine the wet and dry ingredients, mixing until just combined. Do not overmix.
Pour the batter into the prepared loaf pan. Bake for 45 minutes or until a toothpick inserted into the center comes out clean.
Let the loaf cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.