Preheat oven to 350°F/177°C. Grease and flour a 9"x 5" loaf pan or line with parchment paper.
In a small bowl combine all purpose flour, baking powder, poppyseeds and salt. Whisk together to thoroughly combine and set aside.
In a large bowl cream together oil with sugar using a rubber spatula until smooth. Add sour cream, eggs, lemon zest, lemon juice and vanilla. Beat well by hand until mixture is smooth.
Add dry ingredients in 3 parts, mixing until flour is barely visible between each addition. Do not over mix. If there are slight traces of flour still visible after final addition that is okay.
Pour batter into prepared pan and smooth top. Bake for 50-60 minutes or until a toothpick inserted comes out clean. It may take closer to 70 minutes depending on your oven. Allow loaf to cool for 10 minutes in the pan before turning out onto cooling rack.
Prepare glaze only when loaf is cooled completely. Combine confectioner's sugar and lemon juice and beat vigorously by hand until very smooth. Glaze should be quite thick and almost frosting like; add more sugar or lemon juice accordingly. Drizzle back and forth over loaf until entirely covered and smooth out if desired. Allow glaze to set for 1 hour before serving.