1Heat oven to 350°F (325°F for dark or nonstick pan). Grease or spray bottom only of 13x9-inch pan. In large bowl, mix cake mix, butter, water and eggs with spoon. Stir in chocolate chunks. Spread evenly in pan.
2Bake 21 to 26 minutes or until edges are golden brown. Cool completely, about 1 hour.
3In small microwavable bowl, microwave frosting uncovered on High 20 to 25 seconds or until melted; stir. Drizzle over bars. Let stand about 30 minutes or until frosting is set. For bars, cut into 6 rows by 4 rows. Or for triangles, cut bars into 6 rows by 2 rows, then cut each bar diagonally in half to form triangles. Store covered at room temperature.