Add all the wet ingredients to a blender and blend until smooth.
In a large bowl, whisk whole wheat flour, rolled oats, baking powder, lemon zest, and salt.
Pour the blended mixture into the bowl with the dry ingredients. Fold the wet ingredients into the dry ingredients until no dry flour is left - be careful not to overmix.
Cover the bowl with a towel and set aside to rest for 20 minutes.Tip: Soaking the whole grains (whole wheat flour and oats) gives them time to hydrate, creating a thicker batter. This helps the muffins rise better and creates soft, moist muffins.
Preheat oven to 425°F/215°C. Line a muffin pan with paper or silicone liners.
Fold blueberries into the batter.
Scoop the batter into the muffin pan (you should get 9-10 muffins).
Bake for 5 minutes at 425°F, then reduce oven temperature to 350°F/180°C and continue baking another 16-20 minutes until a toothpick inserted in the center of a muffin comes out clean or with cooked crumbs (not wet batter).
Cool muffin pan on a wire rack for 10 minutes, then carefully remove the muffins and place directly on the wire rack to finish cooling.
If serving that day, store in an airtight container at room temperature. Leftovers can be stored in the fridge for about 5 days or in the freezer for 2 months.Tip: These muffins are very moist and since they are lower in sugar and salt (which act as natural preservatives), I don't recommend leaving them out at room temperature overnight. I store mine in the fridge once they are completely cooled.
Notes
1) If you don't want to use bananas, you can use fresh peeled apples or applesauce. Use the same gram measurements (so 180 grams apples or 3/4 cup applesauce).2) These muffins get a lot of their sweetness from the bananas, so I don't add too much extra sugar. I think they taste great with just 3 tablespoons of sugar, but if you like your muffins sweeter you can add an extra 1-2 tablespoons.3) You can use fresh or frozen blueberries. Fresh blueberries tend to burst more easily in the oven while frozen blueberries stay more intact. No need to thaw frozen blueberries.