In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, salt and lemon zest.
Add the vegetable shortening to the dry ingredients and use a pastry cutter or your fingers to cut the vegetable shortening into the flour until the mixture resembles coarse crumbs.
Add oat milk, lemon juice and vanilla. Mix until just combined.
Gently fold in poppy seeds.
Turn dough out onto a lightly floured surface. Shape it into a rectangle that is about 1 inch thick.
Chill the dough in the fridge for about an hour or the freezer for 30 minutes.
While your dough is chilling, preheat your oven to 400°F. Line some baking sheets with parchment paper. You might need 2 or 3 baking sheets, and you may have to bake in multiple batches.
After your dough has chilled, cut it into triangular wedges. Place the wedges on your prepared baking sheets, leaving space between each scone so they can expand a bit.
Bake for 15-18 minutes, or just until the bottoms and edges start turning a bold grown.
Allow the scones to cool before adding the glaze.
After your scones have cooled, whisk together all of your glaze ingredients until smooth. Drizzle lemon glaze over vegan lemon poppy seed scones.