Place2 ½ oz poppy seeds in a small bowl and pour 4 oz whole milk over the seeds. Set aside to soak for at least 1 hour and up to 3 hours.
Preheat the oven to 350 °F. Butter and flour a 12 cup muffin pan or line with paper cupcake liners.
Use the large holes of a box grater or the large grating disc of a food processor to shred 16 oz yellow squash. Spread the squash in an even layer on a paper towel and cover with another paper towel. Press to absorb the liquid. Let the squash sit while you mix the batter.
Combine 10 oz all-purpose flour, 1 ½ teaspoons baking powder, ½ teaspoon salt and 8 oz granulated sugar in a mixing bowl and whisk to combine.
In another bowl, whisk together 1 ¾ oz vegetable oil and 3 large eggs. Stir the squash, finely grated zest from 2 lemons and ½ teaspoon lemon extract into the wet ingredients.
Add the wet ingredients to the dry ingredients all at once and stir just until combined. Drain and rinse the poppy seeds and fold them into the batter.
Use a 2 ounce scooper or 1/4 cup measure to portion the batter into the prepared pan. Bake until the muffins spring back when lightly pressed in the middle, 12-15 minutes
While the muffins bake, combine 1 ½ oz fresh lemon juice and 4 oz confectioner's sugar to make the glaze.
Cool the muffins in the pan for 5 minutes. Lift each still-warm muffin from the tin and dip the top into the lemon glaze. Set on a cooling rack. The glaze will set as the muffins cool.