Preheat the oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease the cups lightly.
In a large bowl, whisk together the flour, sugar, poppy seeds, baking powder, and salt until well combined.
In a separate medium bowl, whisk together the milk, vegetable oil, eggs, vanilla extract, lemon zest, and lemon juice until smooth.
Pour the wet ingredients into the dry ingredients. Stir gently with a spatula until just combined. Do not overmix; the batter should be slightly lumpy.
Divide the batter evenly among the 12 muffin cups, filling each about 3/4 full.
Bake in the preheated oven for 18 to 20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven and allow them to cool in the pan for 5 minutes. Then transfer them to a wire rack to cool completely before serving.