Heat the oven to 400°F and line a baking sheet with parchment.
Whisk the flour, granulated sugar, baking powder, and salt. Cut in the cold vegan butter until the mixture looks like coarse crumbs.
Stir in the plant milk just until a shaggy dough forms. Turn it onto a lightly floured surface and pat it into a rectangle.
Mix the brown sugar and cinnamon. Sprinkle over the dough, fold it in half, and gently pat it back into a rectangle.
Cut the dough into eight wedges and arrange them on the baking sheet. Brush lightly with plant milk.
Bake for 16 to 18 minutes, until the edges are lightly golden and the centers feel set. Cool briefly.
Whisk the powdered sugar with the glaze plant milk and drizzle over the warm scones.