1. Preheat oven to 400 degrees. Position rack in the center of the oven.
2. In a large bowl whisk together the egg, milk, yogurt, oil and lemon peel.
3. Sift the flour, sugar, baking powder and salt onto the liquid ingredients. Using a fork, stir very lightly, just until ingredients are combined.
4. Gently fold in the blueberries. Pour the batter into an 8- or 9-inch baking pan coated with nonstick spray.
5. In a small bowl combine the topping ingredients. Sprinkle evenly over the cake batter.
6. Bake a 400 degrees for 30 to 35 minutes or until the top is lightly browned and a wooden toothpick inserted in the center comes out clean.
7. Allow the cake to cool in the baking pan on a wire rack for at least 10 minutes.
8. Serve warm or at room temperature.
When tightly wrapped in plastic wrap, this coffee cake will keep for 3 to 4 days in the refrigerator. It also freezes very well.