Heat oven to 350F. Grease and flour 8 inch square baking pan.
Stir together flour,sugar,cocoa,baking soda and salt in large bowl. Add water,oil,vinegar and vanilla; beat with spoon or whisk just until batter is smooth and ingredients are well blended. Pour into prepared pan.
Bake 35 to 40 minutes or until wooden pick inserted in center comes out clean. Meanwhile, make topping by adding all toppin ingredients in small bowl until well blended, it makes 1 cup of topping.
When cake is done spread topping mixture over warm cake. Set oven to broil; place pan about 4 inches from heat. Broil 3 minutes or until top is bubbly and brown. Remove from oven. Cool completely in pan on rack.