Preheat the oven to 375˚F. Place oven rack in the middle position. Line a 12-cup muffin tin with paper liners. You can also use nonstick cooking spray to grease the pan, if you prefer.
In a large bowl, whisk together flour, sugar, poppy seeds, baking powder, baking soda, and salt. Set aside.
In a separate medium bowl, whisk together yogurt, lemon juice, lemon zest, eggs, and vanilla until combined. Pour wet mixture into the dry ingredients, stirring until just combined.
Pour in melted butter. Stir together until just combined. It is ok if there are a couple of flour streaks in the batter. Just make sure not to over mix the batter.
Scoop the batter into the prepared muffin tin, evenly dividing the batter between the 12 cups.
Bake for 20 to 25 minutes, until the edges are golden brown and the middles are set. A toothpick inserted into the center should come out clean.
Let muffins cool while you make the glaze. To make the glaze, whisk togetehr powdered sugar and lemon juice until smooth. Drizzle over muffins.
Store muffins in an airtight container at room temperature for up to 3 days. You can also freeze them for up to 3 months*.