Heat oven to 350°F. Coat a 13 x 9 x 2-inch baking pan with nonstick cooking spray. Set aside.
Combine cake mix, sour cream, eggs, vegetable oil and lemon zest in a large bowl. Beat on low speed for 30 seconds, then on medium-high for 2 minutes. Fold in the 1-1/2 cups cranberries. Pour batter into prepared baking pan.
Bake at 350°F for 30 minutes.
In a medium-size bowl, whisk together the flour, brown sugar, cinnamon, nutmeg and salt. Stir in butter until mixture is moistened and starts to clump together.
Carefully remove cake from oven. Sprinkle crumb evenly over the top. Scatter with remaining chopped cranberries. Return crumb-topped cake to oven; bake at 350°F for an additional 20 minutes. Remove pan to wire rack and cool completely.
Dust lightly with confectioners sugar and cut into 16 squares.
