Preheat the oven to 350 degrees.
Combine flour, baking powder, baking soda, and salt in a large bowl.
Stir dry ingredients together to ensure the baking powder and baking soda are mixed in.
If using coconut sugar, stir into the dry ingredients.
Add the apple sauce, lemon juice, lemon zest, vanilla extract, and oat milk. Also, add maple syrup if used instead of coconut sugar.
Stir by hand; do not use an electric mixer.
Do not over-stir; make sure all the ingredients and wet ingredients create a thick and slightly lumpy batter.
Next, gently fold the blueberries into the batter.
Using a silicone bread pan or a pan lined with parchment paper, pour bread batter into the pan, scraping down the bowl's sides to get all the batter.
Then, place ½ cup of blueberries on top of the bread, randomly placing them. This is just for added flavor and aesthetics.
Cook for 50-55 minutes. If using a silicone pan, check the bread at 45 minutes since it cooks quickly.
To check to make sure the bread is cooked through, place a knife through the middle. It should come out clean. If there is batter on the blade, cook for an additional 5 minutes.