Preheat the oven to 350 degrees. Coat a muffin tray with cooking spray.
Combine the flour, baking powder, salt, cinnamon, and 1 tablespoon of lemon zest in a small bowl.
Using a hand mixer, beat the bananas, eggs, brown sugar, melted butter, lemon juice, and vanilla until well blended. Stir in the dry ingredients until just combined, then carefully add 1 cup blueberries and gently mix.
Scoop the batter evenly into the muffin tray.
Sprinkle the remaining blueberries evenly over the tops of each muffin, and press them down a little.
Combine the sugar and the remaining tablespoon of lemon zest, then sprinkle evenly over each muffin.
Place in the oven and bake for 25-27 minutes or until a tester inserted in the center comes out clean.
Remove from oven and cool on a wire cooling rack for a few minutes. Enjoy.