Preheat oven to 375°F (190°C). Grease muffin tin or line with muffin tin liners. (These are so tender that they would be easier to handle if baked in muffin tin liners, although it’s definitely not necessary.)
Mix flour, baking powder, baking soda, poppy seeds, and salt in medium bowl; set aside.
Beat butter and sugar with electric mixer on medium-high speed until light and fluffy, about 2 minutes. Add lemon zest to butter-sugar mixture. Add egg and beat well. With a wooden spoon, stir in half of dry ingredients, followed by one-third of yogurt. Stir in remaining dry ingredients in two batches, alternating with yogurt, until incorporated.
Scoop batter evenly in to prepared muffin tin cups. Bake until muffins are golden brown, 20 to 25 minutes. While muffins are baking, heat 1/4 cup granulated sugar and lemon juice in small saucepan until sugar dissolves and mixture forms light syrup, 3 to 4 minutes. Remove from heat and set aside.
When muffins are done baking, allow to cool in muffin tin for 5 minutes. Remove muffins from tin and place on a wire rack. Generously brush the top of each muffin with glaze. Serve immediately.