Preheat the oven to 350℉. Spray a 9x13-inch dish with nonstick spray.
In a large bowl, whisk together the brownie mix, oil, eggs and water until smooth; pour into the prepared dish. Bake until brownies are done, 28 to 31 minutes. Let the brownies cool.
In a medium bowl, use an electric mixer to combine the powdered sugar, peanut butter and ½ cup butter until smooth. Spread over the cooled brownies.
In a microwave-safe bowl, melt the chocolate chips and butter in bursts of 30 seconds, stirring after each, until smooth and all melted. Drizzle over the peanut butter layer. CHILL in the refrigerator, and then cut into squares.