1. Adjust oven rack to middle position and heat oven to 375 degrees. Grease 12-cup muffin tin.
2. Whisk flour, 1 cup sugar, poppy seeds, baking powder, baking soda, and salt together in large bowl. In second bowl, whisk yogurt, eggs, and lemon zest together until smooth. Fold yogurt mixture into flour mixture with rubber spatula until just combined. Fold in melted butter. (Batter can be refrigerated in covered container for up to 24 hours.).
3. Using greased 1/3-cup measure, divide batter among muffin cups. Bake until golden brown and toothpick inserted in center comes out clean, 25 to 30 minutes, rotating pan halfway through baking.
4. Meanwhile, combine remaining ¼ cup sugar and lemon juice in small saucepan. Cook over medium heat until slightly thickened and syrupy, about 3 minutes. Let muffins cool in pan for 5 minutes, then flip out onto wire rack. Brush with warm syrup and let cool for 10 minutes before serving.