Preheat the oven to 350 degrees. Spray a loaf pan (8 1/2 by 4 1/2) with cooking spray and set aside.
In a medium bowl whisk together the flour, baking powder, and salt. Set aside.
In another medium sized bowl, add sugar and lemon zest. Stir together. Add greek yogurt, milk, olive oil, vanilla, egg and egg whites, poppyseed and whisk vigorously until blended.
Add the flour mixture to the wet mixture and mix until just incorporated. Pour into the prepared pan and bake for 45-50 minutes or until toothpick entered in center comes out clean. Remove and let cool to room temperature.
To make the lemon glaze:
In a small bowl, whisk together powdered sugar, lemon juice, and milk. Pour over the top of the pound cake.