Preheat oven to 400 degrees F (200 degrees C). Spray a 12-cup muffin tin with cooking spray.
Combine all-purpose flour, whole-wheat flour, sugar, baking powder, lavender, and salt together in a bowl. Mix bananas, milk, canola oil, and egg together in a separate bowl. Add banana mixture to flour mixture; stir until just combined. Fold in blueberries. Spoon batter into prepared muffin tin.
Bake in the preheated oven until golden and a toothpick inserted in the center comes out clean, about 20 minutes. Cool muffins in tin for 5 minutes before transferring to a wire rack.