In 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.