Preheat oven to 350℉. Prepare a 12-cup muffin pan with cooking spray or liners.
Make flax egg in a small bowl. Combine water and flax meal, stir, and let sit for 5 minutes.
Peel, remove the seeds, and grate the cucumber using the large holes of a grater (or use a food processor to gently pulse).
Whisk the sugar, oil, and vanilla extract in a large mixing bowl for 1-2 minutes, until well combined.
Gently fold in the flax egg and shredded cucumber.
In another large bowl, mix together the flour, baking powder, baking soda, cinnamon and salt.
Add your blueberries to the flour mixture and gently stir to coat them in flour.
Fold the flour mixture into the sugar mixture and stir just until combined. (If the batter is too dry, add 1-2 tbsp of plant-based milk.)
Fill prepared muffin cups 3/4 of the way full.
Bake for 25-30 minutes. Check with a toothpick after 25 minutes. If the toothpick comes out clean, remove from oven. Let the muffins sit for about 5 minutes before removing them to finish cooling on a cooling rack.