1. Preheat oven to 350°.
2. Combine first 3 ingredients in a medium bowl. Grate rind, and squeeze juice from lemon to measure 1 teaspoon and 2 tablespoons, respectively. Stir rind and juice into batter just until blended. Spoon batter into an 8-inch square baking dish coated with cooking spray. Pour boiling water over batter (do not stir).
3. Bake at 350° for 28 minutes. Remove from oven; let stand 5 minutes. Spoon cake into 8 individual serving bowls; top with berries and whipped topping, if desired. Serve warm.