For streusel filling, combine all ingredients and set aside.
Preheat oven to 375 degrees F. Combine cake mix, eggs, sour cream, oil, water, sugar and flour in a large mixer bowl. Beat at medium speed for 3 minutes with electric mixer.
Pour 1/2 of batter into a greased 13 by 9-inch pan. Sprinkle streusel filling on top and swirl the filing. Spoon remaining batter evenly over filling. Bake for 30 minutes or until a toothpick inserted in the center comes out clean. Cool in pan 25 minutes invert onto serving plate, cool completely.
Combine sugar, milk and lemon juice in bowl. Whisk until smooth. Drizzle over cake.