Preheat the oven to 350°F (180°C). Spray a muffin tray very well with non-stick spray and set aside.
Sift the flour into a mixing bowl and add the sugar, baking powder and salt.
Prepare your vegan buttermilk by adding 1 Tablespoon lemon juice into a measuring jug and then adding soy milk up to the 1 cup (240ml) line. Allow to sit for a minute to curdle.
Peel and mash the banana. Add the coconut oil and mash it up with the banana.
Add the vegan buttermilk, mashed banana and coconut oil and vanilla extract to the dry ingredients and mix in. Don't overmix. The batter should be thick.
Add 1 cup of blueberries to a bowl. Add 1 teaspoon of flour and toss with the blueberries to lightly coat them with flour. This, along with the thickness of the batter will prevent your blueberries from sinking.
Add the blueberries to the batter (leaving behind any excess flour) and fold in gently. Divide the batter evenly between the muffin partitions of the prepared muffin tray.
Add the remaining half cup of extra blueberries directly to the top of muffins, around 2 or 3 to the top of each.
Place into the oven and bake for 20-25 minutes or until lightly browned and they pass the toothpick test i.e. a toothpick inserted into the center of one of the muffins comes out clean (or mostly, if the toothpick hits a blueberry it won't be entirely clean, but you should still get a sense of whether they are done or not).
Allow to cool for a few minutes before removing the muffins from the muffin tray and placing onto a wire cooling rack to cool completely.