Preheat the oven to 350°F. Spray a muffin tin with nonstick cooking spray.
In a large mixing bowl, combine the flour, salt, baking soda, and baking powder. Whisk to combine.
In the bowl of a stand mixer with a paddle attachment, cream together the butter and sugar until light and fluffy.
To the butter and sugar mixture, add eggs, one at a time, beating well after each addition. Scrape down the sides of the bowl as needed.
Mix in the lemon juice, lemon zest, and vanilla.
With the mixer on low, alternate adding some of the flour mixture with Greek yogurt, beginning and ending with the flour mixture.
Fold in the poppy seeds until just incorporated.
Divide the batter evenly between the 12 muffin cups, filling each about ⅔ full. (A 2-tablespoon scoop works great for this.)
Bake 15-20 minutes, or until an inserted toothpick comes out clean with a few crumbs but no wet batter. Allow them to cool for a few minutes before removing them from the muffin tin.
Let the muffins cool on a rack for about 10 minutes before adding the glaze.