Line an 8x4-inch loaf pan with parchment paper and lightly spray with non-stick spray, set aside.
In a large bowl or the bowl of a stand mixer, beat the egg, granulated sugar, vegetable oil, Greek yogurt, buttermilk, vanilla extract, lemon juice and lemon zest on low speed until combined.
In a medium-sized bowl, whisk together all-purpose flour, baking soda, baking powder, salt and poppy seeds.
On low speed, carefully and slowly mix the flour mixture into the wet ingredients until the batter is smooth. Do not overmix.
Pour the batter into the prepared loaf pan and bake for about 40-50 minutes, or until an inserted wooden toothpick comes out clean. Loosely tent with aluminum foil halfway through.
Place on a wire rack to let the loaf cool completely.
In a small bowl, whisk together the powdered sugar, lemon juice and lemon zest. Add more lemon juice depending on how thick you want the glaze. Drizzle over the top of the cooled bread.
Slice and serve.
Notes
Cover and store leftover bread at room temperature for 1 day or in the refrigerator for up to 1 week.