Preheat the oven to 350°F. Line a muffin tin with muffin liners.
Combine flaxseed meal and water in a small bowl. Set aside for 5 minutes to thicken.
In a large bowl, whisk together flaxseed meal, peanut butter, non-dairy milk, maple syrup, coconut oil, vanilla extract, and apple cider vinegar. Add buckwheat flour, oats, lemon zest, baking powder, cinnamon, and salt. Use a wooden spoon or spatula to combine until a smooth batter forms. Fold in blueberries.
Fill each muffin liner 3/4 full. Top with a few more blueberries if desired. Bake for 25-30 minutes until toothpick inserted comes out clean (a few moist crumbs is ok). Allow cooling for 5 minutes before transferring to a wire cooling rack. (Optional): Drizzle over a powdered sugar icing.