Whisk sugar, cornstarch, and salt together in a small saucepan. Set aside.

Using a blender stick, process blueberries until almost smooth, but not liquidy.

Add a quarter cup of blueberry puree plus lemon zest to saucepan. Heat over medium heat until mixture thickens, about five or six minutes or longer, stirring occasionally. Remove from heat and allow to cool slightly.

Add remaining blueberries, lemon juice, and cinnamon and mix gently to combine. Let sit for about 10 minutes. Meanwhile, prepare cake.

Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).

In the bowl of a mixer, beat oil, sugar, and eggs on medium-high until light and fluffy, about three minutes. Reduce speed and alternately add dry ingredients with sour soy milk. Add lemon zest, lemon juice, and vanilla and mix together well.

Spray a Bundt pan with baking spray and dust generously with flour. Pour half of the batter into the pan.

With a knife, make a shallow indentation in the center of the batter all around (forming a circle). Spoon half of the filling into it. Using a knife, make S shapes, gently marbleizing the blueberry mixture into the batter. Repeat with remaining batter and remaining blueberry puree. Be careful to swirl the knife shallowly this time.

Bake for one hour, or until knife inserted comes out clean. Cool for at least half an hour before removing from pan. Cool completely before glazing.

Combine all ingredients in a small bowl. Drizzle over cake. Garnish with additional lemon zest if desired.