In a large bowl, whisk together the flour, poppy seeds, sugar, baking powder, and salt, set aside.
In a medium bowl, whisk together the milk, lemon juice, lemon zest, egg, melted butter, and vanilla.
Pour the wet ingredients into the dry until combined, but do not overmix, if it is a little lumpy that is okay. Let the bowl sit on the counter for 5 minutes.
Heat a skillet over medium to medium-high heat. Spray with cooking spray.
Pour 1/4 - 1/3 cup of the batter onto the hot skillet, spread the batter out a little on the sides.
Let cook until you start to see bubbles forming in the center of the pancake, about 3-4 minutes, flip the pancake over and cook an additional 2 minute or until cooked through in the center.
Repeat with the remaining batter.
To make the glaze, whisk together the powdered sugar, lemon juice, and vanilla in a small bowl.
Serve the pancakes with the glaze and/or maple syrup.