Heat oven to 350°F (325°F for dark or nonstick pan). Grease and lightly flour bottom and sides of 15x10x1-inch pan, or spray with cooking spray.
In large bowl, mix cake mix, peanut butter, water and eggs with spoon. Stir in toffee bits. Spread evenly in pan.
Bake 20 to 25 minutes or until golden brown. Immediately sprinkle chocolate chips over hot bars. Let stand about 5 minutes or until chips are melted; spread evenly. Cool completely, about 1 hour. For bars, cut into 10 rows by 6 rows. Store covered.