Preheat oven to 400 degrees. Line 12 standard muffin tins with paper liners.
In a large mixing bowl, whisk together flour, sugar, salt, baking powder, baking soda and poppy seeds; Set aside.
In a medium mixing bowl, stir together the vegetable oil, lemon juice, lemon zest, egg, vanilla, and buttermilk. Stir into the flour mixture until just combined (do not overmix). Allow batter to sit for 5 minutes.
Spoon batter into the prepared baking tin. Bake 15 minutes, then lower the oven temperature to 325 degrees, and continue to bake 10 minutes, or until golden brown and a toothpick inserted in the center comes out clean. Allow muffins to cool in pan for 10 minutes before removing them to a wire rack.
Meanwhile, make the glaze. Whisk 2 tablespoons of the lemon juice with powdered sugar in a small bowl. Slowly add just enough lemon juice to thin the glaze to a thick, but pourable consistency. Use a fork to drizzle muffin tops with glaze.