Preheat the oven to 375 degrees. Cream the butter and brown sugar until light and fluffy. Mix in the banana and egg. Combine the flour, baking powder, baking soda, salt and lemon peel. Blend into the banana mixture by hand until just moistened. Do not over blend. Gently fold in the blueberries. Line LARGE muffin cups with paper liners. Coat the liners lightly with vegetable spray. Fill each cup a little more than half full. Bake until muffins test done with a wooden toothpick (20-25 minutes)