Preheat the oven to 350 degrees and grease a standard metal loaf pan (9x5 inches or 8 1/2x 4 1/2). You can also line the pan with parchment paper for easy removal, but I like the golden edges it gets without lining it.
In a large bowl, whisk together the soy milk, sugar, lemon zest, lemon juice, lemon extract (if using), melted vegan butter and vanilla until well combined.
To the bowl with the wet ingredients, add the flour, baking powder and salt. Stir until just combined, being careful not to over mix or your bread will be dense.
Rinse the blueberries, then toss them with the flour in a small bowl. This will help them not sink to the bottom of the pan while baking.
Fold the blueberries into the batter, gently.
Pour into the prepared pan, place in the center rack of the oven and bake for 60-75 minutes, or until a toothpick inserted in the middle comes out clean with no wet batter.
Cool in the pan for about 30 minutes, then carefully remove from the pan and transfer to a cooling rack with parchment paper below (to catch the glaze drippings).
Glaze: In a small bowl, whisk together the melted vegan butter, powdered sugar, lemon juice and vanilla until smooth. Pour over the loaf and allow to set for 20-30 minutes if possible. Slice and serve.