Preheat oven to 300°.
Combine brownie mix and water; stir until well blended. Spoon batter into a 9- inch pie plate coated with cooking spray. Bake at 300° for 12 minutes or until done. Cool completely on a wire rack.
Combine ice cream and next 3 ingredients, stirring just until swirled. Spoon into brownie crust. Cover and freeze at least 8 hours.
Spread whipped topping over ice cream.