Preheat oven to 425 degrees Fahrenheit. Spray a muffin tin with non-stick spray or line it with cupcake liners and set aside.
Whisk the 3 cups all-purpose flour, 3 tablespoons poppy seeds, 1 tablespoon baking powder, ½ teaspoon baking soda, and ½ teaspoon salt in a medium bowl.
Using a hand or stand mixer, whisk the 1 cup light brown sugar, ½ cup + 2 tablespoons butter, and 1 tablespoon lemon zest on medium speed until light and fluffy.
Add 2 large eggs, one at a time, mixing until combined. Reduce the speed to low and add the flour mixture and 1 ½ cups plain Greek yogurt, alternating yogurt, flour, yogurt, flour, and yogurt. (DO NOT OVER MIX or your muffins will turn out hard and tough) Gently stir in 1 cup fresh blueberries.
Pour the batter evenly into the muffin cups and bake for 5 minutes. Reduce temperature to 375 degrees Fahrenheit and bake for 15-18 minutes until the muffins are golden brown and an inserted toothpick comes out mostly clean.
Whisk together the 1 cup powdered sugar, 1 ½ tablespoons lemon juice, and 1 teaspoon vanilla. Pour over cooled muffins and serve.