Preheat oven to 220°C (428F) and line muffin pan with muffin liners.
Sift and mix dry ingredients (flour, baking powder, baking soda, salt) and set aside.
Place oil and sugar in a bowl of a stand mixer fitted with the paddle attachment and mix until combined. Add lemon juice and lemon zest and mix for 1 minute.
Add dry ingredients, alternating with milk and mix until just combined. Do not overmix.
Fold in poppyseeds using a spatula.
Divide batter between muffin pan, filling all the way to the top for a large muffin or ¾ full for a smaller muffin.
Bake in a preheated oven at 220°C (428F) for 7-8 minutes. Without opening the oven door, reduce the temperature to 175°C (350F) and bake for another 10-13 minutes until a skewer inserted into the center comes out clean.
Allow muffins to cool in muffin pan for at least 10 minutes (otherwise they may break apart). Then, transfer to a cooling rack to cool completely and drizzle with optinal glaze.
To make the glaze: mix powdered sugar with 2-4 tbsp. of lemon juice until desired consistency is reached. For a thicker glaze, add more powdered sugar. For a thinner glaze, add more lemon juice. Drizzle over cooled muffins.