Heat oven to 350°F. Line 15x10x1-inch pan with foil. Spread nuts in pan. Bake uncovered 6 to 10 minutes, stirring occasionally, until light brown. Pour into small bowl; set aside. Set aside pan with foil to use in step 3.
Meanwhile, in heavy 2-quart saucepan, cook sugars, butter and water over medium-high heat 4 to 6 minutes, stirring constantly with wooden spoon, until mixture comes to a full boil. Boil 20 to 25 minutes, stirring frequently, until candy thermometer reaches 300°F or small amount of mixture dropped into ice water forms a hard brittle strand.
Stir in 1/2 cup of the nuts; immediately pour toffee into same foil-lined pan. Quickly spread mixture to 1/4-inch thickness with rubber spatula. Sprinkle with chocolate chips; let stand about 1 minute or until chips are completely softened. Spread softened chocolate evenly over toffee. Sprinkle with remaining nuts.
Refrigerate about 30 minutes or until chocolate is firm. Break into pieces. Store in tightly covered container.