Muffins:

1 1/2 cups all-purpose flour
2 teaspoons baking powder
1/2 teaspoons salt
1 egg
1/2 cup sugar
3 tablespoons nonfat vanilla yogurt
1 tablespoon canola oil
1/2 cup skim milk
1/2 teaspoon grated lemon rind (optional)
1 1/2 cups blueberries

Preheat oven to 400°F. Coat a 12 cup muffin pan with no-stick spray. In a medium bowl, whisk together the flour, baking powder and salt. In a large bowl, combine the egg, sugar, yogurt, oil and vanilla. Using an electric mixer beat on medium-high for 2 minutes. Reduce the speed to low and alternately beat in the flour mixture and the milk in 4 additions, ending with the milk. Beat just until combined. Stir in the lemon rind. Fold in the blueberries. Divide the batter evenly among the muffin cups, filling them about two-third full. Top each muffin with 1 teaspoon of the topping.

Bake for 17 - 20 minutes or until a toothpick inserted into a muffin comes out clean. Cool on a rack 5 minutes. Remove from pan.

Topping:

In a small bowl, stir together the flour, oats, brown sugar and cinnamon. Cut in the butter until the mixture resembles coarse meal.