Preheat the oven to 350 degrees F. Line a 12-cup muffin pan with paper liners. Using a vegetable peeler, remove the zest from the lemon in wide strips, being careful not to remove the white pith. Combine the lemon zest and sugar in a food processor and process until the zest is finely chopped, scraping the bowl halfway through, about 1 minute. Stir in the poppy seeds. Scoop out 3 tablespoons of the lemon-poppy seed sugar and set aside.
Whisk the flour, baking soda, baking powder and salt in a large bowl. Whisk the remaining lemon-poppy seed sugar, the vegetable oil, buttermilk, vanilla and eggs in a medium bowl; stir into the flour mixture until just combined. Stir in the zucchini.
Divide the batter among the muffin cups, filling them three-quarters of the way. Tap the bottom of the pan lightly on the counter to smooth out the batter. Sprinkle the tops of the muffins with the reserved lemon-poppy seed sugar. Bake until the muffins are golden brown around the edges and a toothpick inserted into the center comes out clean, 23 to 25 minutes. Let the muffins cool 5 minutes in the pan, then remove to a rack to cool completely.